HIP
Head-in-Pillow
HIP is a defect in which BGA solder balls and board paste do not sufficiently coalesce, leaving the joint interface separated or incomplete.
In context
Separation due to warpage during heating, oxidation, flux, contact conditions, and other factors can be involved. A simple ball-presence inspection may not readily detect it.
Example
Even if balls and solder appear to touch again after cooling, an intermittent open can occur if they have not formed a sufficient metallurgical joint.
Key distinction
Distinguish apparent contact from complete coalescence.
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