Quest for perfect Surface Finish Markus Leitgeb Programme Manager, R&D

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Austria Technologie & Systemtechnik Aktiengesellschaft | Fabriksgasse13 | A-8700 Leoben Tel +43 (0) 3842 200-0 | E-mail [email protected]

Agenda

Requirements for the PCB Surface Which surfaces are available ? Cost of surfaces & Cost Driver Enviromental & Recycling Surface Recommendations from AT&S

Surface Finishes / Markus Leitgeb

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Requirements for the PCB surface Major Decision drivers Application ?

Shelf Life ? Rework ?

Solderability ?

Wire Bond process ?

Cost? Mechanical Requirements ?

Surface Finishes / Markus Leitgeb

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Agenda

Requirements for the PCB Surface Which surfaces are available ? Cost of surfaces & Cost Driver Enviromental & Recycling Surface Recommendations from AT&S

Surface Finishes / Markus Leitgeb

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Surface finish - OSP Widely used surface finish for all kinds of products +Easy and „cheap“ process +Even surface +Very well known +Very robust solder joint -More assembly issues due to LF requirements -Not suitable for wire bonding or contact pads -Inspection Thickness: Thin ones (one solder step) 0,1µm; „normal ones“ 0,2µm to 0,5 µm

Surface Finishes / Markus Leitgeb

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Surface finish - HAL Very common surface finish for automotive and industrial applications +Very cheap and easy process +Very reliable +Very easy to solder +Shelf life +Less problems -Uneven surface (thickness range from 1to 40 micrometer) -Thermal shock for PCB -Environmental issues (Lead Free) -Not suitable for small design and contact pads or wire bonding Thickness: HAL on pad 1 – 40 µm, edge of holes should be covered

Surface Finishes / Markus Leitgeb

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Surface finish – Immersion Tin More and more common surface finish for industrial and automotive applications (replacement for HAL) +Very even surface +Good solder joint reliability +Lead free +Easy to solder +Perfect for pin in or press fit -Complex and expensive process -Aggressive chemistry (attacks solder mask) -Sensitive to contamination -Not suitable for contact pads Thickness: 0,8 to 1,2µm; For LF applications 1,0 to 1,4µm is preferred) Surface Finishes / Markus Leitgeb

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Surface finish – Immersion Silver Used for industrial and automotive applications ( North America) +Very even surface +Easy process (compared to ENIG+Imm Tin) +Good solderjoint reliability +Easy to solder +Lead free +Not aggressive process +Suitable for wire bonding -Risk of tarnishing (must be packed within short time) -Sensitive to sulfur -Not suitable for contact pads -Studies show that there is the risk of migration, especially in the precence of copper Thickness: 0,15 to 0,4µm Surface Finishes / Markus Leitgeb

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Surface finish - ENIG Very popular surface finishing for all kinds of PCB (industrial, automotive, telecom application) +Even surface +Reworkable (solderpaste misprinting) +Long storage time +„Easy“ to solder +Multi reflow approved +Can be used for wire bonding +For soldering and contact pads -High process costs (Chemistry and long cycle time) -Process is very complex -Ni-Corrosion/Black pad -Risk of brittle solder joint (Too much Au in solder, P content,…) -For small BGAs solderjoint reliability is lower as on other surfaces Thickness: Ni thickness normally 3 – 6 µm, Au thickness 0,05 to 0,12 µm Surface Finishes / Markus Leitgeb

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Surface finish - ENEPIG Ceramic substrates (LTCC‘s) with thick film coating (Ag paste) are widely used for high temperature applications in the automotive industry e.g. for Transmission Control Units (TCU), Electronic Power Steering (EPS) and Electronic Stability Control (ESP; ECS/ABS). The interconnection between the substrate and the components is usually formed by AuAu-wire bonding (Thermosonic Bonding; Ball-Wedge Bonding) and AlAl-wire bonding (Ultrasonic Bonding; Wedge-Wedge Bonding)

Surface Finishes / Markus Leitgeb

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ENEPIG - Motivation to Replace LTCC

Cost (LTCC format 8”x8”, PCB format 18”x24”)

Supplier base – competitive environment (Limited capacities; LTCC suppliers predominantly in high cost locations)

Lead time (Initial set up time for LTTC is high)

Surface Finishes / Markus Leitgeb

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Challenges to Produce “Wire Bond Boards”
No solder mask (no protection)
Single card handling (