OMIKRON IMMERSION WHITE TIN. Florida CirTech, Inc. Greeley, Colorado USA. Revised 2/19/98

Transcription

1 OMIKRON TM IMMERSION WHITE TIN Revised 2/19/98 Florida CirTech, Inc.

2 C T Florida CirTech, Inc North 17th Avenue Greeley, CO Telephone: Fax: (970) Table of Contents Pages I. Introduction 1-2 II. Comparison of OMIKRON TM to other alternative coatings 3-4 III. Comparison of OMIKRON TM to conventional immersion tin 5-8 IV. OMIKRON TM process A. Vertical mode 9 B. Horizontal mode 10 V. Characterizing the OMIKRON surface-sera A. The SERA unit 11 B. Typical SERA scan 12 C. OMIKRON TM thickness as a function of time and temp. 13 VI. Summary of test results 14 VII. Conclusions 15

3 Introduction Solder Mask Over Bare Copper (SMOBC) has become the preferred manufacturing method for producing printed circuit boards today. The solder coating of the finished boards using Hot Air Leveling (HAL) has led some manufacturing designs to be pushed to the limit. Today s finer pitch and demand for flatter pads have pushed the industry to search for HAL alternatives. As a leading manufacturer of chemicals and materials for the printed circuit board and electronic assembly industry, Florida CirTech has devoted a large amount of time and energy in developing an alternative to HAL that satisfies both industries it serves. The result of this is OMIKRON TM, a novel immersion tin coating that satisfies and in many cases exceeds the requirements expected of a SMOBC coating. OMIKRON TM is used in either a vertical or horizontal mode. It has been used extensively in Europe for over two years, and is now being well received by board manufacturers, assemblers and OEMs in the United States. To summarize, OMIKRON TM has the following characteristics: Property Result 1. Superior solderability at final assembly No clean fluxes and solder pastes work and wet well 2. Flat and uniform surface Less bridging on fine pitch 3. Very long shelf life Wide operating window 4. Withstands multiple heat cycles Wide operating window 5. Can test quality and thickness of coating Feedback on deposit quality Process control 6. Capable of being electrically tested Boards tested after FAB prior to assembly 7. Optically apparent Immediately diagnose any copper surface problems prior to coating 8. One metal system No introduction of metals that can poison wave solder pot 9. Wide plating window User friendly for PCFAB shops 10. Cost effective Economically acceptable as a viable HAL replacement by OEMs -1-

4 OMIKRON TM IMPROVED IMMERSION WHITE* TIN PROCESS DESIGNED AS A REPLACEMENT COATING FOR HOT AIR LEVELING BENEFITS : * COMPATIBLE WITH ALL ASSEMBLY FLUXES AND SOLDER PASTES * EASE OF OPERATION * CAPABLE OF PASSING MULTIPLE ASSEMBLY CYCLES * UNIFORM FLAT AND DENSE SOLDERABLE SURFACE * MEETS AND EXCEEDS SIEMENS SHELF- LIFE TEST ( 4 HOURS AT 155 C ) * NO POISONING OF ASSEMBLER S SOLDER POT * PERFECT FOR FINE PITCH APPLICATION * COST EFFECTIVE COATING * IBM TECHNICAL REPORT -2-

5 COMPARISON OF COATINGS TM PROPERTIES OMIKRON HAL Ni/Au ORGANIC SILVER FINE PITCH APPLICATIONS YES PROBLEM YES YES YES FLATNESS OF PAD YES NO YES YES YES MULTIPLE SOLDERABILITY YES YES YES PROBLEM YES ELECTRICAL TESTING YES YES YES PROBLEM? WASTE TREATMENT MEDIUM HIGH MEDIUM LOW HIGH DIMENSIONAL STRESS NONE HIGH NONE NONE NONE CONTROLLABILITY HIGH LOW MEDIUM HIGH MEDIUM VERTICAL AND HORIZONTAL PROCESSING YES YES NO YES NO COST FACTOR MEDIUM MEDIUM HIGH MEDIUM HIGH COMPATIBLE WITH YES YES NO NO YES ALL FLUX SOLDER POT NO NO YES NO NO CONTAMINATION SOLDER MASK YES YES PROBLEM YES YES COMPATIBILITY REWORKABILITY YES YES PROBLEM PROBLEM PROBLEM SHELF LIFE LONG LONG LONG MEDIUM MEDIUM -3-

6 Thickness Of Finishes in Micro Inches H Hot Air Leveling: O OMIKRON White Tin G Electroless Gold P Electroless Palladium S Electroless Silver T Thick OSP t thin OSP H O G P S T t -4-

7 OMIKRON TM TO IMPROVE LONG TERM SOLDERABILITY ENHANCED DISPLACEMENT REACTION MECHANISM Cu 6 Sn 5 Sn (WHITE TIN) OMIKRON REACTION O Cu + Sn +2 Cu 3 Sn Sn (GRAY TIN) -5-

8 COMPARISON OF IMMERSION TINS SEM PHOTOS OF DEPOSITS OMIKRON WHITE TIN TM COMMERCIAL GRAY TIN FINE GRAIN HEXAGONAL CRYSTAL LARGE GRAIN ORTHORHOMBIC CRYSTAL -6-

9 COMPARISON OF IMMERSION TINS TM OMIKRON WHITE TIN COMMERCIAL GRAY TIN LONG TERM SOLDERABILITY STABLE DENSE FINE GRAIN HEXAGANOL CRYSTAL STRUCTURE SHORT TERM SOLDERABILITY UNSTABLE POROUS LARGE GRAIN ORTHORHOMBIC CRYSTAL STRUCTURE -7-

10 Comparison Of Immersion Tins White Tin, OMIKRON Tin TM Sn O Cu 6 Sn 5 Copper Commerical Gray Tin Sn O 2 Tin Cu 3 Sn Copper NOT DRAWN TO SCALE -8-

11 OMIKRONTM Immersion Tin Process Flow 10% 2-4 min F Water Rinse 1-2 min. CirEtch 100 Micro-Etch 1Lb./gal sec F Water Rinse 1-2 min. OV-4 Pre-Dip 25% 1-2 min F OA-8 Immersion Tin 100% 30 seconds room temp 55-80F OA-8 Immersion Tin 100% 8-9 min F Water Rinse (warm) 2-4 min. Water Rinse 1-2 min. -9-

12 Florida CirTech, ECI and PILL. A winning team to support your conveyorized OMIKRON process. -10-

13 The ECI Model QC-100 Surface-Scan Analysis of OMIKRON TM Immersion Tin Coating The ECI Model QC-100 Surface-Scan incorporates two applications used for the evaluation of the protective effectiveness and conditions of Omikron TM immersion tin coating. These tests are performed on the SMT pads or inside of the through holes. 1. Quick Check (Non - destructive analysis of tin coating surface conditions) This application is used for non-destructive determination of the surface conditions of the immersion tin coating using Sequential Electrochemical Reduction Analysis (SERA). Surface oxides such as SnO, SnO 2 and oxidized Cu-Sn intermetallics (if any) will be accurately detected and quantified. Other compounds or contaminants will be also detected. During this quick test (2-3 minutes), all reducible species (oxides etc.) are removed from the tin surface. 2. Detailed Analysis (Electrochemical oxidation of tin coating) This analysis provides the information about the thickness of tin coating and the amount of underlying copper-tin intermetallic compounds. During this test, the layers of coating are slowly dissolved into the test electrolyte from the small area on the surface tin deposit (1.6 mm diameter). A typical scan is shown for an OMIKRON sample on the next page. Additional QC-100 Applications: *Surface analysis of a copper substrate prior to the placement of the final finish (HASL, etc.) *Detection of oxides, sulfides and other contaminants *Surface analysis of tin/lead coatings *Evaluation of gold deposit cleanliness Hardware and Software Specifications The analytical system consists of the following: *IBM PC compatible QC-100 Analyzer *Measuring Stand for analysis of boards up to 15" x 24" (larger sizes optional) with single test head used for analysis of PTHs or SMT pads *HP color printer *Pressure regulator with flow meter for monitoring inert gas consumption *User-friendly software running in MS-Windows 3.X or Windows 95 *Data storage in MS Access format (MS Access Included) -11-

14 ImmersionTin Electrochemical OxidationTest Oxidationof e-phase Oxidation of n-phase Oxidationof tin coating Time (sec) -12-

15 OMIKRON thickness as a function of time and temperature Thickness(Microns) Min 6 Min 9 Min Run number OMIKRON (Virgin) Tin Thickness(Microns) Run # Temp(F) 3 Min 6 Min 9 Min

16 Summary of OMIKRON TM testing Test Purpose Result 1. SIR testing Pass SIR? Pass 2. Electromigration Dendritic and Tin Whiskers? Pass 3. Solder Wettability tests Determine solderability of OMIKRON is #1 OMIKRON versus HAL and Silver coating. 4. Heat Cycling tests Pass. Multiple reflow cycles? Pass(3or more)heat cycles. 5. Microetch dependence Surface preparation dependence Wide window 6. Tin conc., specific Determine solution operating Wide window gravity, ph and copper. Window conc. test 7. Immersion time and Determine immersion time Characterization temperature test dependence 8. Aging test Determine degradation of Acceptable up to 24 hours. OMIKRON as aged at 107C up to 24 hours. 9. Coplanarity and Thirty six samples run. Excellent results for OMIKRON Reproducibility study 10. Rework Simulation Thirty two samples run. Pass for non-aged and aged samples. 11. Ionic contamination OMIKRON versus HAL Pass 12. Microsection analysis Solderability aged and non- Pass aged. Note: SERA: Selective Electrochemical Reduction Analysis Tests 1-3 performed by Trace Laboratories. Tests 4-7 performed by Florida CirTech. Tests 8-12 performed by Parlex and Florida CirTech. -14-

17 Conclusion OMIKRON TM is the clear choice as the superior alternative to hot air leveling. It provides excellent solderability, a flat and uniform surface, a shelf life of over one year and is easy to test. OMIKRON TM avoids all the problems associated with other alternative coatings with a cost that is competitive with or lower than the rest. OMIKRON TM is a white tin rather than the traditional gray tin and thereby provides a more dense, fine grain crystal structure. OMIKRON TM has excelled both in laboratory tests and in actual use in PCFAB and assembly shops throughout the United States and Europe. Facilities using OMIKRON TM will have a competitive advantage over those using other coatings. For more information, please contact your local Florida CirTech sales representative or our main office at