Application Report. Donald C. Abbott, Stu Grenney, Larry Nye, Douglas W. Romm... SLL Logic ABSTRACT

Transcription

1 Application Report Whisker Evaluation of Pb-Free Component Leads Donald C. Abbott, Stu Grenney, Larry Nye, Douglas W. Romm... SLL Logic ABSTRACT Integrated circuits (ICs) with both tin-lead (SnPb) and Pb-free finished leads were tested for whisker growth susceptibility. Some of the ICs were built at TI assembly sites, while others were obtained from assembly/test (A/T) subcontractors. The conditions used to promote whisker growth were typical for the industry, 51 C and 51 C + 85% relative humidity (RH). In addition, these same conditions were imposed on board-mounted ICs that had a 5-V bias applied to adjacent leads. Recently, industry consortia and standards groups have narrowed recommended whisker test conditions to a suite of tests. However, testing reported here was initiated prior to a recommended set of conditions being adopted. The results of these tests were both expected and surprising. Very limited whisker growth was seen on SnPb-finished units, which is comparable to what is being reported in the industry. Nickel-palladium-gold (NiPdAu) finish did not demonstrate any whisker growth, which is as expected. We found whiskers on some matte-sn-finished components and no whiskers on other matte-sn-finished components, similar to our previous experience. SnBi finish did not demonstrate whisker growth, contradicting our previous results. Bright Sn and matte Sn with brass base metal did whisker as expected. Nickel (Ni) underplate did not have a mitigating effect on whisker growth at extended read points. Annealing did not mitigate whisker growth. However, in all cases where whisker growth was seen, the maximum length did not exceed 45 µm, which is the Technology Acceptance criteria listed by JEDEC (at the time of this writing, August 2005). This paper highlights results seen on whisker testing of several SnPb and Pb-free finish options on various IC packages. NiPdAu is the only finish that consistently showed no whisker growth. Sn-based finish options showed varying results, but any whiskers seen met current JEDEC acceptance criteria. Industry is not in complete agreement on the JEDEC Sn-whisker acceptance criteria. Contents 1 Introduction Test Method Whisker Inspection Results Summary of Results References List of Figures 1 Isometric View of SOIC (D) Gullwing Package Isometric View of SOT (DCK) Gullwing Package Isometric View of PDIP (N) Through-Hole Package Isometric View of TO-92 (LP) Package Isometric View of QFN (RGQ) Package Isometric View of TO-220 (KV) Through-Hole Package Isometric View of TO-263 (KTT) Through-Hole Package... 7 Whisker Evaluation of Pb-Free Component Leads 1

2 8 SOIC Unit From Subcon S1 Soldered to PWB Inspection Locations for SOIC (D) and SOT (DCK) Units Inspection Locations for PDIP (N) Units Inspection Locations for TO-92 (LP) Units Inspection Locations for QFN (RGQ) Units Inspection Locations for TO-220 (KV) Units Inspection Locations for TO-263 (KTT) Units Typical Grain Structure on Group 1, SnPb SOIC Unit, 1500 Magnification Typical Grain Structure on Group 2, SnPb PDIP Unit, 1500 Magnification Typical Grain Structure on Group 3, NiPdAu SOIC Unit, 1500 Magnification Typical Grain Structure on Group 4, NiPdAu PDIP Unit, 1500 Magnification Typical Grain Structure on Group 5, Matte-Sn SOIC Unit, 1500 Magnification Typical Grain Structure on Group 9, SnBi DCK, 1500 Magnification Typical Grain Structure on Group 10, Bright-Sn SOIC Unit, 1500 Magnification Typical Grain Structure on Group 11, Matte-Sn SOIC Unit, Brass Base Metal, 1500 Magnification Typical Grain Structure on Group 12, SnCu TO-92 Unit, 1500 Magnification Typical Grain Structure on Group 13, 0.5Ni + Whisker-Sn SOIC, 1500 Magnification Typical Grain Structure on Group 14, 0.5Ni + Whisker-Free Sn SOIC, 1500 Magnification Typical Grain Structure on Group 15, Matte-Sn (Whisker-Sn) SOIC, 1500 Magnification Typical Grain Structure on Group 16, Matte-Sn (Whisker-Free Sn) SOIC, 1500 Magnification Typical Grain Structure on Group 19, Annealed Matte-Sn TO-220, 1500 Magnification Typical Grain Structure on Group 20, Matte-Sn TO-220, 1500 Magnification Typical Grain Structure on Group 21, Annealed Matte-Sn TO-263, 1500 Magnification Typical Grain Structure on Group 22, Matte-Sn TO-263, 1500 Magnification Typical Grain Structure on Group 23, Annealed Matte-Sn TO-92, 1500 Magnification Group 2 PDIP SnPb Finish at 10000, 51 C/85%RH No Bias, 2000-h Exposure, Whisker Length µm Group 2 PDIP SnPb Finish at 45000, 51 C/85%RH + Bias, 2000-h Exposure, Whisker Length 0.46 µm Group 3, SOIC NiPdAu Finish, 51 C/85%RH No Bias, 3000-h Exposure, No Whiskers Noted Group 3 SOIC NiPdAu Finish, 51 C/85%RH + Bias, 3000-h Exposure, No Whiskers Noted Group 4 PDIP NiPdAu Finish, 51 C/85%RH No Bias, 3000-h Exposure, No Whiskers Noted Group 4 PDIP NiPdAu Finish, 51 C/85%RH + Bias, 3000-h Exposure, No Whiskers Noted Group 6 SOIC Matte-Sn Finish at 2000, 51 C/85%RH + Bias, 2000-h Exposure, Whisker Length 5.36 µm Group 6 SOIC Matte-Sn Finish at 3000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 9.7 µm Group 8 PDIP Matte-Sn Finish at 4500, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 10.3 µm Group 8 PDIP Matte-Sn Finish at 6000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length µm Group 10 SOIC Bright-Sn Finish at 10000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 4.93 µm Group 10 SOIC Bright-Sn Finish at 3500, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length µm Group 11 SOIC Matte-Sn Finish, Brass Base Metal at 1500, 51 C/85%RH + Bias, 2 Whisker Evaluation of Pb-Free Component Leads

3 3000-h Exposure, Whisker Length 29.4 µm Group 12 TO-92 SnCu Finish at 23000, 51 C/85%RH No Bias, 2000-h Exposure, Whisker Length 3.2 µm Group 12 TO-92 SnCu Finish at 13000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 2.39 µm Group 13 SOIC 0.5 Ni + Whisker Sn at 2000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length µm Group 13 SOIC 0.5 Ni + Whisker Sn at 3300, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length µm Group 14 SOIC 0.5 Ni + Whisker-free Sn at 3000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 9.53 µm Group 14 SOIC 0.5 Ni + Whisker-Free Sn at 4000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 7.53 µm Group 15 SOIC Whisker Sn at 9000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 2.52 µm Group 15 SOIC Whisker Sn at 1200, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length µm Group 16 SOIC Whisker-Free Sn at 3700, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 3.67 µm Group 16 SOIC Whisker-Free Sn at 8500, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 2.52 µm Group 17 QFN Sn Finish With SnPb Paste on PWB at 3000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 4.17 µm Group 18 QFN Sn Finish With SnAgCu Paste on PWB at 4300, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 3.95 µm Group 19 TO-220 Annealed Matte Sn at 3500, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 29.2 µm Group 19 TO-220 Annealed Matte Sn at 25000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 3.21 µm Group 20 TO-220 Matte Sn at 15000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 4.2 µm Group 20 TO-220 Matte Sn at 1800, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 14.2 µm Group 21 TO-263 Annealed Matte Sn at 13000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 2.6 µm Group 21 TO-263 Annealed Matte Sn at 8000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 5.1 µm Group 22 TO-263 Matte Sn at 3500, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 10.3 µm Group 22 TO-263 Matte Sn at 5000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 8.2 µm Group 23 TO-92 Annealed Matte Sn at 5000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 16.4 µm Group 23 TO-92 Annealed Matte Sn at 7000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 5.81 µm List of Tables 1 Tin-Whisker Growth Test Recommendations Source and Plating Details for Each Package Evaluated NEMI Definitions of Matte-Sn and Bright-Sn Finishes Whisker Test Matrix NEMI/JEDEC Whisker Classification Categories SEM Inspection Summary for All Groups Whisker Evaluation of Pb-Free Component Leads 3

4 Introduction 1 Introduction There are various lead (Pb)-free finish options available for use (or already in use) by integrated circuit (IC) manufacturers. Nickel-palladium-gold (NiPdAu) is a finish that has been in use for leadframe packages for several years.[1, 2, 3] NiPdAu is a pre-plated finish, meaning that the plating is applied to the leadframe prior to assembly (die attach, mold encapsulation, etc.) of the IC package. Tin (Sn) finish is the predominant finish being offered by IC manufacturers who utilize post-mold plating operations. Other options are Sn alloys, including tin-copper (SnCu) and tin-bismuth (SnBi). A concern with plated Sn and Sn-based alloys is Sn-whisker growth. There is no generally accepted universal Sn-whisker growth theory, despite Sn whiskers being recognized for more than 50 years.[4] It is fairly well established that compressive stress in the Sn layer is a driver for Sn-whiskers, but the source of the stress is still being debated. For Cu base metal terminations, Cu migration into Sn grain boundaries, leading to formation of Cu 6 Sn 5 intermetallics, is a probable cause of stress in the Sn. But, oxidation from the top of the Sn layer into the Sn grain boundaries may also induce stress. Recent studies have shown oxidation/corrosion of the Sn by exposure to high humidity leads to accelerated Sn-whisker formation. The Sn-oxidation effect is independent of base metal. Alloy-42 based terminations show Sn-whisker growth after thermal cycling, most likely caused by the CTE mismatch between the alloy-42 and the Sn. The mechanism for Sn atom movement to the Sn whisker to relieve the stress in the Sn layer and feed the Sn whisker is under lively discussion now; no clear mechanism has been established at this writing. In the recent inemi sponsored Tin Whisker Workshop held in conjunction with the Electronic Components and Technology Conference 2005, the statement was made several times There is no magic bullet to solve the Sn-whisker problem. Confounding the research on Sn whiskers is the contradictory data in the industry concerning the effectiveness of whisker mitigation techniques such as Ni underplate, annealing, reflow, and grain orientation.[5, 6] In 2002, TI performed whisker evaluations on matte-sn finished ICs.[7] In that study, whisker test results were not as expected and were contrary to much of the literature. Whiskers were seen on some matte-sn finished components and no whiskers on other matte-sn finished components. Whiskers were seen on some larger Sn-grain deposits, and no whiskers were seen on some finer-grain deposits. This study was begun in late 2003, with analyses concluded in early Test conditions used in this study included exposure to 51 C/85%RH with and without bias. This set of conditions originally was developed by TI in 2002, based on inputs from industry consortia. The conditions of 51 C/85%RH demonstrated whisker growth on samples tested in In mid-2004, the National Electronics Manufacturing Initiative (NEMI) recommended a suite of test conditions based on multiple designed experiments.[8] This set of test conditions eventually was refined and published in JEDEC standard JESD22A121.[9] A note included in JESD22A121 indicates that the document is not a qualification standard, but, rather, contains a suite of recommended Sn-whisker growth tests. This set of tests includes the conditions shown in Table 1. When the set of TI testing in this report was begun, the NEMI/JEDEC conditions had not been refined; thus, the historical conditions of 51 C/85%RH were used. Table 1. Tin-Whisker Growth Test Recommendations RECOMMENDATIONS STRESS TYPE TEST CONDITIONS INSPECTION MINIMUM INTERVALS DURATION Minimum temperature: 55 C to 40 C (+0/ 10) C, Temperature cycling Maximum temperature: 85 C (+10/ 0) C air to air, 500 cycles 1000 cycles 5 to 10 min soak, 3 cycles/h Ambient temperature/humidity storage 30 C ± 2 C and 60 C ± 3 C 1000 h 3000 h High temperature/humidity storage 60 C ± 5 C and 87 C (+3/ 2) C 1000 h 3000 h 4 Whisker Evaluation of Pb-Free Component Leads

5 1.1 Components Evaluated Introduction Many whisker-mitigation techniques have been proposed by experts in the industry. Recent recommendations have included use of matte Sn, use of a Ni underplate, and annealing of the Sn plating.[10, 11, 12] The purpose of this study was to evaluate whisker test performance of the primary Pb-free finish options using recommended whisker mitigation techniques. SnPb-finished components were used as a control for comparison. Several IC packages were chosen for this evaluation. Packages were built both at TI assembly sites and IC assembly subcontractors external to TI. Plating thickness was measured for each component type. Grain size was measured both before and after whisker test exposure. Grain size shown after test exposure is an average of grain size with and without bias conditions. Key details of each package/finish option evaluated are shown in Table 2. Table 2. Source and Plating Details for Each Package Evaluated PLATING GRAIN SIZE, GRAIN SIZE, GROUP PIN A/T THICKNESS NO TEST 3000-h PACKAGE FINISH NO. COUNT CODE (µm, EXPOSURE EXPOSURE MEASURED) (µm) (µm) 1 16 SOIC S1 SnPb PDIP S1 SnPb SOIC TI NiPdAu Per TI spec (1) NMGS (2) NMGS (2) 4 16 PDIP TI NiPdAu Per TI spec (1) NMGS (2) NMGS (2) 5 16 SOIC S1 Matte Sn SOIC S1 Matte Sn (from study 1) SOIC S2 Matte Sn PDIP S1 Matte Sn DCK S3 SnBi SOIC S1 Bright Sn (whisker) NMGS (2) NMGS (2) SOIC S1 Matte Sn (brass) TO-92 S4 SnCu NMGS (2) NMGS (2) SOIC S1 0.5Ni + whisker Sn SOIC S1 0.5Ni + whisker-free Sn SOIC S1 Matte Sn (whisker) SOIC S1 Matte Sn (whisker-free) QFN S1 Sn (SnPb paste) NA (3) QFN S1 Sn (SnAgCu paste) NA (3) TO-220 S5 Annealed matte Sn 8.48 (4) TO-220 S5 Matte Sn 8.74 (4) TO-263 S6 Annealed matte Sn TO-263 S6 Matte Sn TO-92 S5 Annealed matte Sn 9.10 (4) (1) NiPdAu units met TI specification for plating thicknesses. (2) NMGS indicates that no measurable grain size was detected. (3) NA indicates that samples not available for plating thickness measurement. (4) Measured by X-ray fluorescence The first four columns indicate the group number, pin count, package type, and IC package assembly site (coded). Groups coded TI were built at a TI internal assembly site. Groups coded with S1, S2, etc., were built at an external assembly subcontractor. Column 5 shows details of the component finish for each group. Column 6 shows plating thickness measured by cross section (or where indicated by X-ray fluorescence). Columns 7 and 8 show the average grain size for each group prior to and after whisker test exposure. Whisker Evaluation of Pb-Free Component Leads 5

6 Introduction Eight different types of lead finish are in this study. These represent a broad spectrum of available or proposed finishes to comply with Pb-free requirements. Descriptions of each type of finish follow. Devices with tin-lead (SnPb) post-mold plated leads are included in this work as controls. The SnPb finish was the predominant Sn-bearing lead finish for electronic components prior to the European Pb-free initiatives. The SnPb-finished leads provide a standard for comparison of all the other finishes included here for Sn-whisker susceptibility. Because the SnPb is plated using soluble anodes and has a long history, control of the plated deposit alloy content and thickness are relatively well understood. Devices with nickel-palladium-gold (NiPdAu)-finished leads are in to this study to confirm that there is no propensity for elemental (Pd or Au) whisker growth with this type of finish. The Ni, Pd, and Au are deposited sequentially, resulting in a three-layer deposit. They are not alloyed. Although the extremely thin deposits (approximately 0.01-µm Pd and µm Au) preclude significant stresses to drive whisker growth and, by being so thin, there is little mass to support whisker growth, some customers have asked for data demonstrating NiPdAu performance in a standard whisker test. NiPd and NiPdAu have been evaluated for whiskers in the past and have shown no whisker growth.[7] Leads with a bright-sn finish, bright Sn being defined as a fine-grained deposit with measurable co-deposited carbon content (see Table 3), are included as others have demonstrated bright Sn to have a pronounced tendency to grow Sn whiskers.[4, 10] It was expected that the bright-sn finish would have Sn-whisker growth. Brass base-metal leads with matte-sn finish are in this test matrix, because it has been demonstrated by others that brass, most likely because of its high zinc content, facilitates the growth of whiskers.[4] Matte Sn has been demonstrated to have less propensity for whisker growth than bright Sn. So-called Ni underplate, Ni of 0.5 µm to 2.0 µm deposited on the lead prior to Sn plating, has been touted as a whisker-mitigation technique.[11] The proposed mechanism is that the Ni underplate prevents Cu migration from the base metal into the grain boundaries of the Sn. Conflicting data on this approach has been presented.[10] Not withstanding Ni underplate s efficacy or non-efficacy in reducing whisker propensity, plating Ni after molding and prior to Sn plating presents manufacturing challenges, as the rate of Ni deposition is slow. Slow deposition of Ni translates to either very long plating lines to accommodate plating both the Ni and Sn or a two step process, both of which impact yield and cost of manufacture negatively. Preplating the Ni at the leadframe manufacturing house negatively impacts moisture sensitivity level (MLS) performance, because most widely used mold compounds do not adhere well to Ni surfaces. There are two types of matte Sn included in sample groups 13 to 16, with and without Ni underplate. The Sn-plating deposit behavior, whisker-prone or whisker-free, was determined experimentally by the plating-electrolyte supplier. The characteristics of the deposit were a function of the electrolyte composition and plating conditions. Stress and contamination levels in the Sn were not determined, as they were beyond the scope of this work. Because tin-copper (SnCu)-finished leads are being offered commercially by some in the industry as a Pb-free lead finish, SnCu is included in this work. The SnCu is applied directly to the lead, with no Ni underplate. Others maintain the SnCu would represent the worst approach for a low-tendency whisker finish.[13] Process issues with an SnCu are alloy and thickness control. The percentage of Cu changes the melting point of the SnCu deposit significantly, and assaying alloy percentage is not a simple, straightforward procedure, because the base metal is a Cu alloy. Measuring deposit thickness presents similar problems because of the Cu-bearing base metal. A tin/bismuth (SnBi) is being offered commercially as a Pb-free lead finish, mainly in Japan. The signal advantages of SnBi are that it has low melting point, 150 C, and it has a reasonable history, meaning alloy control is established. The drawback to SnBi is that if Pb is introduced into the solder joint, via Pb-bearing paste, board finish, or repair, a very low melting phase (<95 C) can form, degrading the solder-joint strength. Annealed matte-sn finished leads also are included in this study. Annealing, which promotes grain growth of the Sn and, thus, reduces the likelihood of Sn whiskers developing, has been offered as another mitigation technique.[12] Again, as in the Ni-underplate mitigation technique, conflicting data has been presented on the efficacy of annealing matte Sn to mitigate Sn-whisker growth at the inemi Tin Whisker Workshop, May 31, For the annealed matte-sn samples tested in this study, the annealing conditions were 150 C for 1 hour. Annealing was performed within 24 hours after plating. 6 Whisker Evaluation of Pb-Free Component Leads

7 Introduction Many of the Sn-finished units tested are described as matte finish. The NEMI definitions of matte- and bright-sn finishes are shown in Table 3. Table 3. NEMI Definitions of Matte-Sn and Bright-Sn Finishes PARAMETER MATTE Sn BRIGHT Sn Carbon content 0.005% to 0.50% 0.2% to 0.4% Grain size 1 µm to 5 µm 0.5 µm to 0.8 µm In their definition of bright-sn finishes, NEMI indicated that bright Sn is essentially featureless by scanning electron microscope (SEM) inspection, less ductile, and can be slightly harder than matte Sn. Figure 1 through Figure 7 show isometric views of the various package types evaluated. Figure 1. Isometric View of SOIC (D) Gullwing Package Figure 2. Isometric View of SOT (DCK) Gullwing Package Figure 3. Isometric View of PDIP (N) Through-Hole Package Figure 4. Isometric View of TO-92 (LP) Package Figure 5. Isometric View of QFN (RGQ) Package Figure 6. Isometric View of TO-220 (KV) Through-Hole Package Figure 7. Isometric View of TO-263 (KTT) Through-Hole Package Whisker Evaluation of Pb-Free Component Leads 7

8 Test Method 2 Test Method All groups were exposed to the test conditions shown in Table 4. The test conditions of 51 C/85%RH and 51 C/85%RH + bias were developed by TI in 2002, based upon industry inputs at that time. The set of testing reported in this paper was begun prior to widespread use/acceptance of the NEMI recommended conditions or JEDEC standard JESD22A121. Thus, the historical conditions that were used were the same as in reference 7. Table 4. Whisker Test Matrix RUN BIAS 51 C + 85%RH 1 No Yes 2 Yes Yes The 51 C bake condition has been determined empirically by several researchers to favor Sn-whisker growth. The relative humidity, at 85%, is thought to favor whisker growth by facilitating the growth of Sn oxide on the surface of the Sn. TI included two cells with bias, as this is an in use condition. The applied bias was 5 V. Bias is not typically or widely used in whisker testing, and the impact of bias on whisker growth still is being evaluated. Board mounting allowed biasing the parts. The board-mount reflow process may relax internal stresses in the Sn layer that were present before board mount and, thus, reduce the tendency to whisker in these deposits. 2.1 Sample Mounting Procedure All units subjected to whisker testing were board mounted on PWBs. The solder paste was SnPb, and the reflow profile was typical for SnPb-soldering process, with peak temperature being 220 C. One theory is that higher reflow temperatures (>235 C) seen with Pb-free (SnAgCu) solder alloys may relax the stress in the plating and reduce whiskering. Choice of SnPb paste and reflow temperature for this evaluation was based on the desire to exclude any impact of higher reflow temperature processes. If component suppliers start producing Sn-finished components in volume, there is an undefined length of time when SnPb solders (and associated reflow temperatures) will still be in use by a high percentage of reflow operations. Thus, use of the SnPb-solder process with peak temperature of 220 C as a worst-case condition was justified. The PWBs used for board-mounted SOICs can be seen in Figure 8. Figure 8. SOIC Unit From Subcon S1 Soldered to PWB 8 Whisker Evaluation of Pb-Free Component Leads

9 2.2 Inspection Locations and Procedure Test Method The inspection process was designed to achieve two goals: documenting the standard initial inspection process, inclusive of a grain-size measurement, and the detection of whisker activity. Magnification levels of 450 to 1500 were adopted for the standard initial inspection process, inclusive of a grain-size measurement. Magnification levels of 1500 to were applied for whisker inspections. Magnification levels were adjusted as needed to deal with the wide range of surface-finish and/or whisker-site conditions. Units from each group in Table 2 were inspected for grain size and whisker growth at 0-h and at 2000-h and 3000-h exposure points. The samples in Groups 1 through 16 were scratched on at least one lead prior to testing. Scratching creates localized mechanical stresses in the surface finish and may favor whisker growth. Standard inspection points for the SOIC, SOT, and PDIP units (see Figure 9 and Figure 10) were: 1. Top edge of lead at the shoulder bend (left side) 2. Top center of lead at shoulder bend 3. Center of lateral lead-surface scratched area 4. Bottom-left edge near underside of shoulder bend Standard inspection points for TO-92 (LP), TO-220 (KV), and TO-263 (KTT) units (see Figure 11, Figure 13, and Figure 14) were: 1. Top edge of lead at the shoulder bend (left side) 2. Top center of lead at shoulder bend 3. Left side of lead at the shoulder bend 4. Top edge of lead at the shoulder bend (right side) Standard inspection points for the QFN samples (see Figure 12) were: 1. Left edge of lead at intersect with plastic 2. Top center of lead near plastic package 3. Left edge of lead at intersect with plastic (tilt view) 4. Top center of lead near front edge The locations identified in Figure 9 through Figure 14 were the primary single-point inspection locations observed at the specified magnification. That same location was also the start point of the expanded whisker inspection process. In the expanded inspection the full length of the leads, interfaces, and surface areas of the leads were inspected at increased magnification levels on an as-needed basis. Figure 9. Inspection Locations for SOIC (D) and SOT (DCK) Units Figure 10. Inspection Locations for PDIP (N) Units Whisker Evaluation of Pb-Free Component Leads 9

10 Test Method Figure 11. Inspection Locations for TO-92 (LP) Units Figure 12. Inspection Locations for QFN (RGQ) Units Figure 13. Inspection Locations for TO-220 (KV) Units Figure 14. Inspection Locations for TO-263 (KTT) Units Although this study was initiated prior to the publication of formal guidelines for the measurement and classification of tin whiskers as prescribed by JEDEC and NEMI documents, where possible, results obtained are described per those definitions. Whiskers and non-whisker surface formations reported are grouped into classification categories described in Table 5. It should be noted that extended discussions are currently ongoing as to sample size, both number of leads inspected and total area inspected. CATEGORY Table 5. NEMI/JEDEC Whisker Classification Categories 1 Tin whisker filaments DESCRIPTION 2 Whiskers with a consistent cross-section 3 Kinked whiskers 4 Kinked whiskers growing from a nodule 5 Branched tin whiskers 6 Whiskers initiating from a hillock 7 Tin whisker filaments with striations 8 Kinked whiskers initiating from an eruption 9 Tin whiskers with rings 10 Dendrites 11 Hillocks 12 Flowers 10 Whisker Evaluation of Pb-Free Component Leads

11 2.3 Grain Appearance Test Method Dendrites, hillocks, and flowers (categories 10, 11, and 12) are atypical surface anomalies and are not considered to be tin whiskers. Representative thumbnail photographs of these classification categories can be found in Annex C of Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes.[9] The temperature and humidity conditions applied in this study are very closely aligned with the conditions currently being proposed by JEDEC in JESD201, Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes. For each interval readpoint, the maximum whisker length is recorded and classified. The maximum whisker length is compared against the most stringent maximum length allowed per the proposed JEDEC conditions for Technology Acceptance (45 µm) for temperature and humidity storage. Grain size was measured for the components tested to classify the finish per NEMI recommendations. Examples of the grain structure seen on units from each supplier are shown in Figure 15 through Figure 32. All grain-size photos shown are prior to test exposure. Figure 15. Typical Grain Structure on Figure 16. Typical Grain Structure on Group 1, SnPb SOIC Unit, Group 2, SnPb PDIP Unit, 1500 Magnification 1500 Magnification Figure 17. Typical Grain Structure on Group 3, NiPdAu SOIC Unit, 1500 Magnification Figure 18. Typical Grain Structure on Group 4, NiPdAu PDIP Unit, 1500 Magnification Whisker Evaluation of Pb-Free Component Leads 11

12 Test Method Figure 19. Typical Grain Structure on Figure 20. Typical Grain Structure on Group 5, Matte-Sn SOIC Unit, Group 9, SnBi DCK, 1500 Magnification 1500 Magnification Figure 21. Typical Grain Structure on Group 10, Bright-Sn SOIC Unit, 1500 Magnification Figure 22. Typical Grain Structure on Group 11, Matte-Sn SOIC Unit, Brass Base Metal, 1500 Magnification Figure 23. Typical Grain Structure on Group 12, SnCu TO-92 Unit, 1500 Magnification Figure 24. Typical Grain Structure on Group 13, 0.5Ni + Whisker-Sn SOIC, 1500 Magnification 12 Whisker Evaluation of Pb-Free Component Leads

13 Test Method Figure 25. Typical Grain Structure on Figure 26. Typical Grain Structure on Group 14, 0.5Ni + Whisker-Free Sn SOIC, Group 15, Matte-Sn (Whisker-Sn) SOIC, 1500 Magnification 1500 Magnification Figure 27. Typical Grain Structure on Group 16, Matte-Sn (Whisker-Free Sn) SOIC, 1500 Magnification Figure 28. Typical Grain Structure on Group 19, Annealed Matte-Sn TO-220, 1500 Magnification Figure 29. Typical Grain Structure on Figure 30. Typical Grain Structure on Group 20, Matte-Sn TO-220, Group 21, Annealed Matte-Sn TO-263, 1500 Magnification 1500 Magnification Whisker Evaluation of Pb-Free Component Leads 13

14 Test Method Figure 31. Typical Grain Structure on Group 22, Matte-Sn TO-263, 1500 Magnification Figure 32. Typical Grain Structure on Group 23, Annealed Matte-Sn TO-92, 1500 Magnification Grain structures noted for all matte-sn and annealed matte-sn units (groups 5 to 8 and 13 to 23) could all be classified as large well-polygonized grains. Grain structures on the SnPb and SnBi units were well defined, but smaller in appearance compared with the matte Sn. NiPdAu-, bright-sn-, and SnCu-finished units were essentially featureless, with no grain structure notable. One theory for large grains suppressing whiskers is that stress inherent or induced in the Sn plate is distributed over a larger volume in coarse-grain deposits. This gives a lower stress per unit volume. In a similar fashion, thicker Sn deposits spread the stress over a larger volume, particularly if the stress is associated with SnCu intermetallics close to the Sn/Cu interface and not generally distributed in the Sn layer. The work presented in this report does not support these contentions. We saw whiskers on parts with Sn plating >8 µm and on Sn deposits with large grains. These results point to the complexity of the Sn-whisker phenomenon and suggest that factors such as high internal stress can overcome the cited means to minimize whiskering propensity. 14 Whisker Evaluation of Pb-Free Component Leads

15 3 Whisker Inspection Results Whisker Inspection Results Table 6 summarizes the SEM inspection results for all groups. Data is indicated for all groups, whether or not whiskers were seen for that particular group/run combination. Maximum whisker length was tablulated, and the whiskers were classified per the whisker types outlined in JEDEC standard JESD22A121. Results for the various finish types are discussed in Section 3.1 through Section Table 6. SEM Inspection Summary for All Groups 2000 HOURS 3000 HOURS RUN ID: RUN 1 RUN 2 RUN 1 RUN 2 BIASED: No Yes No Yes 51 C + 85%RH: Yes Yes Yes Yes REV NEW PIN MAX MAX MAX MAX PACKAGE FINISH TYPE TYPE TYPE TYPE GROUP COUNT LENGTH LENGTH LENGTH LENGTH NO SOIC SnPb None 0.00 None 0.00 None 0.00 None PDIP SnPb None 0.00 None SOIC NiPdAu None 0.00 None 0.00 None 0.00 None PDIP NiPdAu None 0.00 None 0.00 None 0.00 None SOIC Matte Sn None 0.00 None 0.00 None 0.00 None 0.00 Matte Sn 6 16 SOIC None , None (from study 1) 7 16 SOIC Matte Sn None 0.00 None 0.00 None 0.00 None PDIP Matte Sn None DCK SnBi None 0.00 None 0.00 None 0.00 None 0.00 Bright Sn SOIC None 0.00 None , (whisker) Matte Sn SOIC None 0.00 None 0.00 None , (brass) 12 3 TO-92 SnCu None 0.00 None Ni SOIC , , , whisker Sn 0.5Ni SOIC whisker-free None 0.00 None Sn Matte Sn SOIC None (whisker) Matte Sn SOIC None , (whisker-free) Sn (SnPb QFN None 0.00 None None 0.00 paste) Sn (SnAgCu QFN None 0.00 None , None 0.00 paste) Annealed 19 5 TO , matte Sn 20 5 TO-220 Matte Sn None , Annealed 21 5 TO matte Sn 22 5 TO-263 matte Sn Annealed 23 3 TO-92 None , , matte Sn Whisker Evaluation of Pb-Free Component Leads 15

16 Whisker Inspection Results 3.1 Inspection Results for SnPb-Finished Units Two groups of SnPb-finished units were tested. Of these two groups, only group 2, the SnPb PDIP units, showed whisker growth. The relatively minimal whisker growth seen (<1 µm) was noted after 2000-h exposure to 51 C/85%RH conditions with and without bias (see Figure 33 and Figure 34). Figure 33. Group 2 PDIP SnPb Finish at Figure 34. Group 2 PDIP SnPb Finish at 10000, 51 C/85%RH No Bias, 45000, 51 C/85%RH + Bias, 2000-h Exposure, Whisker Length µm 2000-h Exposure, Whisker Length 0.46 µm 3.2 Inspection Results for NiPdAu-Finished Units As expected, no whisker growth was seen on the NiPdAu-finished units. Figure 35 through Figure 38 show surface-finish appearance of both NiPdAu-finished SOICs and PDIPs after exposure to 51 C/85%RH with and without bias. Figure 35. Group 3, SOIC NiPdAu Finish, 51 C/85%RH No Bias, 3000-h Exposure, No Whiskers Noted Figure 36. Group 3 SOIC NiPdAu Finish, 51 C/85%RH + Bias, 3000-h Exposure, No Whiskers Noted 16 Whisker Evaluation of Pb-Free Component Leads

17 Whisker Inspection Results Figure 37. Group 4 PDIP NiPdAu Finish, 51 C/85%RH No Bias, 3000-h Exposure, No Whiskers Noted Figure 38. Group 4 PDIP NiPdAu Finish, 51 C/85%RH + Bias, 3000-h Exposure, No Whiskers Noted 3.3 Inspection Results for Matte-Sn-Finished Units Group 5 matte-sn-finished SOICs from subcontractor S1 did not demonstrate whisker growth. However, SOIC units from the same supplier, which were built in the 2002 timeframe (group 6), did show whisker growth when tested in this study. Matte-Sn-finished SOIC units from subcon S2 (group 7) did not demonstrate whisker growth. Matte-Sn-finished PDIP units from subcon S1 (group 8) showed whisker growth at both 2000-h and 3000-h exposure with and without bias (see Figure 39 through Figure 42). Figure 39. Group 6 SOIC Matte-Sn Finish at Figure 40. Group 6 SOIC Matte-Sn Finish at 2000, 51 C/85%RH + Bias, 2000-h Exposure, 3000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 5.36 µm Whisker Length 9.7 µm Whisker Evaluation of Pb-Free Component Leads 17

18 Whisker Inspection Results Figure 41. Group 8 PDIP Matte-Sn Finish at Figure 42. Group 8 PDIP Matte-Sn Finish at 4500, 51 C/85%RH No Bias, 6000, 51 C/85%RH + Bias, 3000-h Exposure, 3000-h Exposure, Whisker Length 10.3 µm Whisker Length µm 3.4 Inspection Results for SnBi-Finished Units The SnBi-finished SOT units from subcontractor S3 did not demonstrate whisker growth in this study. This result contradicts the whisker growth seen on SnBi-finished SOT units tested in 2002.[7] 3.5 Inspection Results for Bright-Sn-Finished Units The bright-sn finished SOIC units from subcontractor S1 (group 10) did show whisker growth after 3000-h exposure to 51 C/85%RH with and without bias (see Figure 43 and Figure 44). Figure 43. Group 10 SOIC Bright-Sn Finish at Figure 44. Group 10 SOIC Bright-Sn Finish at 10000, 51 C/85%RH No Bias, 3500, 51 C/85%RH + Bias, 3000-h Exposure, 3000-h Exposure, Whisker Length 4.93 µm Whisker Length µm 18 Whisker Evaluation of Pb-Free Component Leads

19 3.6 Inspection Results for Sn-Finished Units With Brass Base Metal Whisker Inspection Results The Sn-finished SOIC units with brass base metal from subcontractor S1 (group 11) did show whisker growth after 3000-h exposure to 51 C/85%RH + bias conditions (see Figure 45). Figure 45. Group 11 SOIC Matte-Sn Finish, Brass Base Metal at 1500, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 29.4 µm 3.7 Inspection Results for SnCu-Finished Units The SnCu-finished TO-92 units from subcontractor S4 (group 12) showed whisker growth after 2000-h exposure to 51 C/85%RH and 3000-h exposure to 51 C/85%RH + bias. Examples of the whisker growth seen are shown in Figure 46 and Figure 47. Figure 46. Group 12 TO-92 SnCu Finish at Figure 47. Group 12 TO-92 SnCu Finish at 23000, 51 C/85%RH No Bias, 13000, 51 C/85%RH + Bias, 2000-h Exposure, Whisker Length 3.2 µm 3000-h Exposure, Whisker Length 2.39 µm Whisker Evaluation of Pb-Free Component Leads 19

20 Whisker Inspection Results 3.8 Inspection Results for Ni-Underplate Units Group 13 (0.5Ni + whisker Sn) showed whisker growth in all combinations. Group 14 (0.5Ni + whisker-free Sn) showed whisker growth at 3000 h, both with and without bias. Group 15 and 16 (matte Sn, whisker and matte Sn, whisker-free) showed whisker growth at 51 C/85%RH (2000 h and 3000 h) and at 51 C/85%RH + bias (3000 h) (see Figure 48 through Figure 55). Figure 48. Group 13 SOIC 0.5 Ni + Whisker Figure 49. Group 13 SOIC 0.5 Ni + Whisker Sn at 2000, 51 C/85%RH No Bias, 3000-h Sn at 3300, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length µm Exposure, Whisker Length µm Figure 50. Group 14 SOIC 0.5 Ni + Figure 51. Group 14 SOIC 0.5 Ni + Whisker-free Sn at 3000, 51 C/85%RH No Whisker-Free Sn at 4000, 51 C/85%RH + Bias, 3000-h Exposure, Bias, 3000-h Exposure, Whisker Length 9.53 µm Whisker Length 7.53 µm 20 Whisker Evaluation of Pb-Free Component Leads

21 Whisker Inspection Results Figure 52. Group 15 SOIC Whisker Sn at Figure 53. Group 15 SOIC Whisker Sn at 9000, 51 C/85%RH No Bias, 1200, 51 C/85%RH + Bias, 3000-h Exposure, 3000-h Exposure, Whisker Length 2.52 µm Whisker Length µm Figure 54. Group 16 SOIC Whisker-Free Sn Figure 55. Group 16 SOIC Whisker-Free Sn at 3700, 51 C/85%RH No Bias, at 8500, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 3.67 µm 3000-h Exposure, Whisker Length 2.52 µm Whisker Evaluation of Pb-Free Component Leads 21

22 Whisker Inspection Results 3.9 Inspection Results for QFN Units The Sn-finished QFN units were soldered to a PWB using either SnPb or SnAgCu paste. Both groups of units (Groups 17 and 18) showed whisker growth under 51 C/85%RH at 3000-h exposure. Whisker growth seen was in the exposed leadframe area above the solder joint (see Figure 56 and Figure 57). Figure 56. Group 17 QFN Sn Finish With SnPb Paste on PWB at 3000, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 4.17 µm. Figure 57. Group 18 QFN Sn Finish With SnAgCu Paste on PWB at 4300, 51 C/85%RH No Bias, 3000-h Exposure, Whisker Length 3.95 µm 3.10 Inspection Results for Annealed Matte-Sn Units Groups 19 and 21 (annealed matte-sn TO-220 and TO-263) showed whisker growth in all combinations. Group 20 (matte Sn TO-220) showed whisker growth at 51 C/85%RH (2000 h and 3000 h) and at 51 C/85%RH+bias (3000 h). Group 22 (matte-sn TO-263) showed whisker growth in all combinations (see Figure 58 through Figure 67). Figure 58. Group 19 TO-220 Annealed Matte Figure 59. Group 19 TO-220 Annealed Matte Sn at 3500, 51 C/85%RH No Bias, Sn at 25000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 29.2 µm 3000-h Exposure, Whisker Length 3.21 µm 22 Whisker Evaluation of Pb-Free Component Leads

23 Whisker Inspection Results Figure 60. Group 20 TO-220 Matte Sn at Figure 61. Group 20 TO-220 Matte Sn at 15000, 51 C/85%RH No Bias, 1800, 51 C/85%RH + Bias, 3000-h Exposure, 3000-h Exposure, Whisker Length 4.2 µm Whisker Length 14.2 µm Figure 62. Group 21 TO-263 Annealed Matte Figure 63. Group 21 TO-263 Annealed Matte Sn at 13000, 51 C/85%RH No Bias, Sn at 8000, 51 C/85%RH + Bias, 3000-h Exposure, Whisker Length 2.6 µm 3000-h Exposure, Whisker Length 5.1 µm Figure 64. Group 22 TO-263 Matte Sn at Figure 65. Group 22 TO-263 Matte Sn at 3500, 51 C/85%RH No Bias, 5000, 51 C/85%RH + Bias, 3000-h Exposure, 3000-h Exposure, Whisker Length 10.3 µm Whisker Length 8.2 µm Whisker Evaluation of Pb-Free Component Leads 23

24 Whisker Inspection Results Figure 66. Group 23 TO-92 Annealed Matte Figure 67. Group 23 TO-92 Annealed Matte Sn at 5000, 51 C/85%RH No Bias, 3000-h Sn at 7000, 51 C/85%RH + Bias, Exposure, Whisker Length 16.4 µm 3000-h Exposure, Whisker Length 5.81 µm 3.11 Observations Eight of the 23 groups exhibited distinct grain-boundary whisker growth. Whiskers seen on these groups have clear evidence that they emanated from the surface finish. Another observation was that many of those granular growths had vivid striations along the length of the whisker. The shortest whisker length seen (less than 0.5 µm), requiring the highest magnification levels of 45000, was observed on the Group 2, 16-pin PDIP SnPb-finish units. In contrast, the longest whisker length of 29.4 µm was found at 1500 magnification level on the Group 11, matte-sn-finish SOIC with brass base metal. Significant increase was seen in whisker activity at 3000 h versus that seen at 2000 h. There were 27 whisker detections at 3000 h versus 17 at 2000 h. At 2000 h, 10 non-biased samples and 7 biased samples showed whisker growth. At 3000 h, 13 non-biased samples and 14 biased samples showed whisker growth. Groups 19 (annealed matte-sn TO-220), 21 (annealed matte-sn TO-263), and 22 (matte-sn TO-263) all exhibited grains that appeared to be lifting from the finish surface prior to exposure to the test conditions detailed in Table 4. With reference to the NEMI/JEDEC Whisker Classification Categories (see Table 5), the predominant observed whisker shapes were types 1 and 2 (tin-whisker filaments and whiskers with a consistent cross-section, respectively). No whisker activity was seen on 25% (6 of 24 groups) of the groups inspected. 24 Whisker Evaluation of Pb-Free Component Leads

25 4 Summary of Results 4.1 Conclusions Summary of Results For the SnPb units tested, whiskers were seen with lengths <1 µm using very high magnification. The NiPdAu-finished units showed a smooth surface appearance with no whisker growth. For the matte-sn-finished units (groups 5 to 8), whiskers were noted on two of the four groups. The SnBi SOT units tested did not demonstrate whisker growth, which contradicts performance seen in our earlier study. The bright-sn-finished SOICs showed whisker growth. The Sn-finished units with brass base metal did show whisker growth. The SnCu-finished TO-92 units showed whisker growth. The two groups of units that utilized a Ni underplate did show whisker growth. The plating treatments, as classified by the plating supplier (whisker and whisker-free), did not have an impact, as each group did demonstrate whisker growth. Both groups of QFN units showed whisker growth, independent of the solder alloy used to attach the packages to the PWBs. The whisker growth was seen in the exposed lead area above the solder joint. Both annealed and non-annealed units (TO-220, TO-263, and TO-92) showed whisker growth. The temperature and humidity test conditions in this study (51 C/85%RH) were established in 2003 and were representative of the conditions being considered by the various industry groups studying the problem at that time, specifically NEMI. These conditions also were used by TI in a 2002 whisker study and successfully produced Sn whiskers on several popular lead finishes being used within the industry.[7] The temperature and humidity conditions in the recently approved JESD22A121 document, Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes, are 60 C ± 5 C and 85% to 90% RH as boundary conditions. Likewise, the proposed JEDEC JESD201 standard (Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes, under ballot at the time of this writing) specifies 60 C ± 5 C and 87% (+3/ 2)% RH as the temperature and humidity test conditions. As noted, the temperature and humidity conditions used in this study are closely aligned with those being proffered for industry standard conditions. The proposed JEDEC JESD201 standard (Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes) provides general guidelines defining product classes as follows: Class 1A: Consumer products Class 1: Industrial products Class 2: Business applications (telecom, high-end servers, etc.) Class 3: Mission/life critical (military, aerospace, medical) The most stringent maximum allowable whisker length in the Technology Acceptance Criteria in this proposed document for high-temperature/high-humidity storage is 45 µm for Class 2 products. Note: Pure tin and high-tin-content alloys are not allowed for Class 3 products per this document. In this study, for all that developed whiskers, the whiskers were below the 45-µm maximum length through 3000 h of testing. For consumer products in Class 1A, these results easily meet the Technology Acceptance Criteria for maximum acceptable whisker length. This work was successful in documenting whisker performance of several component finish options. As expected, NiPdAu finish did not grow whiskers. Units finished with SnPb, matte Sn, bright Sn, matte Sn with brass base metal, and SnCu all demonstrated whisker growth in at least one sample. Industryrecommended mitigation techniques of Ni underplate and annealing did not eliminate whisker growth. SnBi-finished units did not show whisker growth in this evaluation, contrary to previous work.[7] This work also included comparison of non-biased and biased units. While this is still a test condition under consideration by industry, this set of test results did not clearly indicate an effect of bias. Finally, while whisker growth was seen on most groups tested, no whisker lengths were noted greater than the current industry Technology Acceptance Criteria. Whisker Evaluation of Pb-Free Component Leads 25

26 References 5 References 1. D. C. Abbott, R. M. Brook, N. McLelland, and J. S. Wiley, Palladium as a Lead Finish for Surface Mount Integrated Circuit Packages, IEEE Transactions on Components, Packaging, and Manufacturing Technology, Vol. 14, September 1991, pp Douglas Romm, Bernhard Lange, and Donald Abbott, Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits, 3. Donald Abbott, Douglas Romm, Bernhard Lange, Ni-Pd-Au Component Lead Finish and Its Potential for Solder-Joint Embrittlement, 4. George Gaylon, Annotated Tin Whisker Bibliography and Anthology, IEEE Transactions on Electronics Packaging Manufacturing, Vol. 28, January 2005, pp Special Issue on Tin Whiskers, IEEE Transactions on Electronics Packaging Manufacturing, Vol. 28, No. 1, January Douglas W. Romm, Donald C. Abbott, Stu Grenney, and Muhammad Khan, Whisker Evaluation of Tin-Plated Logic Component Leads, 8. Tin Whisker Acceptance Test Requirements, inemi Tin Whisker User Group, July 28, 2004, 9. JEDEC Standard JESD22A121, Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes, inemi Tin Whisker User Group,Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products Version 3, Updated May 2005, J. W. Osenbach, R. L. Shook, B. T. Vaccaro, A. Amin, B. D. Pottieger, and K. N. Hooghan, The Effects of Board Attachment Processing on Sn Whisker Formation on Electroplated Matte-Sn on Cu Alloy Lead Frames, P. Oberndorff M. Dittes, P. Crema, and S. Chopin, Whisker Formation on Matte Sn Influencing of High Humidity, 55th Electronic Components and Technology Conference, May 31 - June 3, K. W. Moon, M. E. Williams, C. E. Johnson, G. R. Stafford, C.A. Handwerker, and W. J. Boettinger, The Formation of Whiskers on Electroplated Tin Containing Copper, 26 Whisker Evaluation of Pb-Free Component Leads

27 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI s standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and applications using TI components. To minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right, or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive business practice. TI is not responsible or liable for such altered documentation. Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Following are URLs where you can obtain information on other Texas Instruments products and application solutions: Products Applications Amplifiers amplifier.ti.com Audio Data Converters dataconverter.ti.com Automotive DSP dsp.ti.com Broadband Interface interface.ti.com Digital Control Logic logic.ti.com Military Power Mgmt power.ti.com Optical Networking Microcontrollers microcontroller.ti.com Security Telephony Video & Imaging Wireless Mailing Address: Texas Instruments Post Office Box Dallas, Texas Copyright 2005, Texas Instruments Incorporated