Alpha Solder Paste Addresses Head in Pillow Defects

Posted 03/20/2012 by $username

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Head-in-pillow defects, or incomplete coalescence of BGA sphere and solder paste deposit, is a failure mode that has seen increased frequency since the transition to lead-free soldering.

Often missed during inspection, a head-in-pillow (HIP) defect appears like a small head resting on a pillow with a visible separation in the solder joint at the interface of the BGA sphere and paste deposit.

HIP Image


This difficulty impacts manufacturers using Ball-Grid Arrays (BGAs), Chip-Scale Packaging (CSP), Solder-Bumped or Stacked Die, and Stacked Package solutions. Left to process engineers to resolve with limited time, resources, and money, head-in-pillow problems lead to electrical contact problems and in some cases do not present themselves as failures until after the device is in service. The issue arises at four key steps in the mounting process, beginning with the original package, at PCB printing, in package mounting, and during reflow. In short, head-in-pillow is result of warpage, alignment, excessive time and temperature reflow profile, and z-axis location, but a robust solution is readily available. 

Cookson Electronic’s ALPHA® Pb-free and halogen-free solder paste can have a great impact on minimizing the occurrence of this defect.

Cookson’s field personnel and Customer Technical Support Engineers are experts in reviewing assembly steps to reverse and prevent the problem. They assist in identifying ways to optimize time, temperature, and alignment. Once processes are optimized and implemented, Cookson further advises using a solder paste that produces taller and more consistent volume deposition, has a greater resistance to longer soak profiles, and has faster wetting speed due to more active flux. ALPHA® solder paste offers all the key features needed to significantly reduce the head-in-pillow defect. All told, Cookson’s ALPHA® products are the result of a dedicated R&D process and can help recapture time, resources, and money for electronic assembly manufacturers in today’s ultra-competitive business environment. 

What are techniques you have successfully implemented to optimize your process to prevent HIP? 

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