Authored By:
Hemal Bhavsar1, Dan Duffy, Bruno Tolla, Ph.D.
Kester, An ITW Company
Itasca, IL, USA
Summary
OSCA materials are dispensable or printable polymeric coating material, which is One Step Chip Attach Coating material designed to form a protective layer around solder joints, which ultimately results into results into reduced corrosion, salt formation, and dendrite growth. Advantages to using this material includes no masking that reduces process time and cost. The material is designed to have controlled flow after dispense, fast cure and simpler process compared to standard conformal coating. It can be dispensed using Jet or Auger technologies, which integrates into existing assembly equipment. There is no need to coat entire device. Device can be selectively coated on most critical areas or areas known to be susceptible to corrosion. After dispensing, this material can be cured in convection oven and can be cured in few minutes between 140-160oC. This paper presents reliability study of highly corrosive printed paste with polymeric coating material and comparing it with conformal coating.
The study was designed to compare a paste that barely passes SIR at 85C/85RH with polymeric coating material, Silicone conformal coating, and acrylic conformal coating. Another part of this study was to study thickness effect on reliability results. Preliminary results show formation of tin salts around traces and some corrosion on uncoated areas, but it was not observed after polymeric coating material was printed on the board. Using this new material as coating prevents formation of salts, corrosion and dendrite growth. Material thickness and volume of material dispensed on the area is very important to obtain optimum results with this polymeric coating material.
Conclusions
OSCA-C materials are designed to be dispensable specific coating material. Advantages to using this material includes faster processing times, fast curing, and no drying step. There is no masking required and minimal volume of material will be required, which end up reducing cost and much faster processing. This study shows that reliability performance can improved using this material. Paste A performed poorly with dendrites and salt formation, but with OSCA-C material it wasn't observed. Using acrylic or silicone conformal coating showed negligible resistivity improvements.
Initially Published in the SMTA Proceedings
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