Introduction to Embedded Passives

Transcription

1 Introduction to Embedded Passives Passive components PTH, SMD, and now embedded passives Form factor, weight, size, height and OEM capability Tolerance values, material compatibility with PWB processing Need to be economical; bulk usage; large volume In handheld products they occupy almost 70% board area and they are almost 50% in component share Current product range require HF/RF compatibility Research integration into industry- seen in mobile market Current status of passive components >30 billion USD worldwide market

2 Discrete IPD Embedded Various types of passives Discrete devices Integrated passive devices (IPD) Embedded (integral) passives Courtesy: KJ Lee, GeorgiaTech

3 Industry impact Source: Nikkei Publications; Nikkei Electronics Asia; May 2003 issue

4 Why Embedded Passives? Improves the packaging efficiency System-on-Package (SOP); SLIM integration Reducing size Eliminating substrate assembly Minimizing solder joint failure and enhancing reliability Faster and cleaner electrical signals Add functionality More design flexibility? Better reliability? Pb-free Cost savings; near-zero incremental cost?

5 Why the reluctance towards embedded Passives? Indecision on Processes and materials Lack of Design Tools Lack of Costing tools Business integration not clear yet Yield and tolerance issues Lack of standardization Surface Mount is improving (0201; 01005)

6 Source: ITRI Technologies Growth

7 Through-hole resistors and capacitors Surface mount devices Embedded concept Source: Wikimedia Commons

8 R+C sample board High K cap PTF resistors FR-4 substrate 8-layer HDI build

9 Source: GeorgiaTech, PRC

10 Fundamentals of Resistors A resistor controls electric current by resisting the flow of charge through itself. Usually it contains a strip of the resisting material with two conducting pads at the ends.

11 The unit of resistance is ohm (!), and it measures how well it resists or opposes the flow of current. It is calculated by using R="L/Wd Where R is the resistance (!), " is the resistivity of material (!-cm), L is the length of the strip (cm), W is the width of the strip (cm) and d is the thickness of the strip (cm). Resistance is dependant on the resistivity of the material and the dimensions of the strip. Higher resistance can be achieved by using higher resistivity materials, increasing the length and using smaller cross-sections. Sheet resistance is the resistance of a square strip. (Sheet resistivity)

12 Source: Richard Ulrich et al; Swapan Bhattacharya; other N2=1 N3=1

13 Basic Resistor Pattern 1. Bar Type a. Multiple Squares (N>/=1) b. Partial Squares (N<1)

14 2. Meander Type A meander resistor can be considered as a bar resistor with the exception of the corner squares (right-angle bends). Due to the change in current density at right-angle path, the effective number of square is Example: Sheet resistance Rs= 100ohms/square No. of squares=37 No. of corner squares-16 Total no. of effective squares= 37+(16 x 0.56) = 45.9 ~46 Resistance value= 46 x 100= 4.6Kohms Source: Richard Ulrich; Swapan Bhattacharya, Ohmega Inc

15 CEDT Design Library

16 Embedded Passives Design, Fab and Test

17 ROUTES TO EMBEDDED RESISTORS Technology Approach Electroless plated Resistor Process (1-1Kohm) Foil Transfer Process (1-1Kohm) SUBTRACTIVE PROCESS Polymer thick film (PTF) Printing Process (500-10Kohms) ADDITIVE PROCESS 1. Synthesis of Ni-P alloys by electroless deposition on dielectrics 2. Electroless plated resistor on epoxy and other polymers (Proprietary chemicals/lab synthesis) 1. Lamination using commercially available resistor foils 2. Laminated thin film resistors on BCB and epoxy dielectrics (Ohmega/Shipley/Gould) 1. Stencil printing using commercial products 2. Lift off Process (Asahi Chemical/Motorola/DuPont) Issues Laser Trim for better tolerance in R values Screen printing of PTF is technician and machine dependant; parameters not always reproducible Choice of Substrate critical for foil transfer process due to Tg and lamination temperatures Electroless Ni-P alloy plating consistency depends on ph, temperature and P concentration in bath

18 Steps for fabrication of Embedded R by PTF Polymer-carbon thick films with suitable sheet resistivity can be used Stencil printing; screen printing or masking by dry film photoresist Source: KJ Lee, Georgia Tech

19 Steps for fabrication of R by foil method and electroless process ) Source: Gould process; KJ Lee, Georgia Tech Cu-NiCr, Cu-NiCrAlSi foils from Gould Electronics used. 25, 50 and 1Kohms/square sheet resistivity Cu thickness- 18microns R Foil thickness- 1 to 2 microns Ni-P or NiWP for electroless R

20 Electroless Bath Formulations for Ni-P Chelating Agents used: Sodium Acetate Bath Sodium Pyrophosphate bath Sodium Citrate Bath Reducing Agent- Sodium Hypophosphite Sodium Acetate Bath Composition Nickel Sulphate : 30 g/l Sodium Hypophosphite : 15 g/l Lead Acetate : g/l Sodium Acetate : 15 g/l Temperature : 90 C ph : 4-5 Sodium Citrate Bath Composition Nickel Sulphate : 26.3 g/l Sodium Hypophosphite : 21.2 g/l Trisodium Citrate : 58.8 g/l Temperature : 90 C ph : 4-5 Sodium Pyrophosphate bath Composition (Solution A & B mixed in equal Proportions) Solution A Nickel Sulphate : 50 g/l Sodium Pyrophosphate : 100 g/l 25 %Ammonium Hydroxide : 200 ml/l Solution B Sodium Hypophosphite : 50g/l Temperature : 30 C ph : ~11 Ni-W-P Composition Nickel Sulphate : 7 g/l Sodium Hypophosphite : 10 g/l Sodium Tungstate : 10 g/l Trisodium Citrate : 45 g/l Temperature : 90 C ph : 4-5 Observations In the Citrate bath, lowering of the concentration of chelating agent, increases the R value. Time, temperature and ph critical to the nature of the deposit.