SUMMARY: UIC CONSORTIUM 2007

Solder Joint Fragility (Pad Finish Issues)
Depending on service conditions 5-10% of all solder joints on Cu pads may develop severe enough voiding in the intermetallics to affect robustness and reliability. We shall improve our recommended test and 'life assessment' procedures, attempt to qualify an apparent remedy, and pursue a complete resolution. The latter will involve a combination of in-depth characterization (TEM, SIMS, ICP, X-ray, EBSD, GDMS,...) of unusually reproducible 'good' and 'bad' Cu samples, and ongoing systematic plating experiments with PCB suppliers. This and other degradation mechanisms (for imm. Ag, Cu(OSP), ENIG, electrolytic Ni/Au) will also be characterized and quantified in solder ball pull/shear as well as assembly level testing.

Printed Circuit Boards
An ongoing effort addresses obvious and subtle/latent damage and degradation of PCBs in no-Pb assembly (effects of reflow, component and solder properties, ambient exposure, handling, aging, ...). So far over 50 laminates and flex materials were tested in various designs of 2-32 metal layer structures. Test procedures and criteria, as well as guidelines for optimizing pad adhesion/robustness in drop, will be developed.

2^nd Level Assembly, Repair & Reliability
Work will still address SnPb but emphasize no-Pb and mixed SnPb/no-Pb with quality defined by joint and pad life/robustness in thermal excursions and, increasingly, mechanical loading (drop, bending, ...).

No-Pb Solder Assembly & Reliability
SAC alloys (1-4%Ag & 0.5-1%Cu w/wo Ni, Co, Zn, .., additions) will be characterized. New dependencies of drop, bending and thermal cycling performance on history, process, alloy, pad finish, solder volume... and their interactions will be quantified. Common thermal cycling tests are potentially very misleading, but obvious 'improvements' require prohibitively long testing times. Instead, a major data base will be established and used to recommend practical test protocols and correction factors to apply to results. Limitations and potential pit-falls will be documented.

Mixed no-Pb/SnPb Solder Assembly & Reliability
The behavior of mixed solders is proving much more complex even than no-Pb and strong scatter or apparent irreproducibility is common. A considerable data base will be further expanded and used to update process recommendations. Special attention will be paid to whether current thermal cycling results may be strongly misleading because of interactions between mixing ratio, process, and dwell times. Emphasis will, however, also here be placed on drop, bending, etc.

Mechanical (Isothermal) Testing
A generic understanding will be developed of how damage in drop depends on height/acceleration, span, component and PCB parameters, etc. Possible correlations between drop, bending/torsion, and testing of individual balls will be addressed, as will synergistic effects of aging, ambient exposure, drop, cycling, ... Solder joint strength and pad robustness will be optimized through alloy selection and modification, process, and PCB design.

Component Underfilling
Preferred solutions depend on component and substrate properties, access, and required balance between thermal cycling and shock resistance. Pros and cons of full and partial capillary flow, no-flow, and corner only (pre- and post-assembly dispense) underfilling will be quantified. Preferred materials will be identified and generic guidelines developed.

Medical Electronics
Ongoing projects emphasize very high density, light weight, double sided assemblies and synergistic effects of thermal history, mechanical loads and ambient exposure. Mechanical robustness is optimized and quantified. Attempts are made to address extreme failure statistics (ultimate reliability).

Flip Chip Assembly & Reliability
Ongoing work will update our comprehensive guidelines on design, materials selection, process, and reliability. Emphasis will be on new underfills (particularly no-flows and wafer applied) and lead free solders (SnCu, maybe others).

Thermal Interface Assembly
We shall develop guidelines for materials selection and optimization of thermal interface assembly processes in terms of porosity, voiding, and filler particle distributions, as well as sensitivity to aging, humidity, cycling, .., measuring thermal performance in-situ with patterned RTDs for selected materials.

Practical Deliverables
Yield assessment tools. Solder reliability data. No-Pb PCB materials data. Guidelines ('cook-books'): no-Pb assembly, mixed solder, repair, PCB testing for no-Pb, component underfilling, double sided assembly, MLF assembly, flip chip, thermal interface assembly, thermal cycling assessment of no-Pb, drop testing.