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I know it’s been a while since my last post, but we’ve been so busy. In fact, one such incident was yesterday. One of our VP’s came to me and asked me to do a 10-15 slide presentation on head-in-pillow defects (Also called “Hidden Pillow” or Ball-in-Cup (BIC) defects). Sure, no problem. So, last afternoon, we’re on a conference call with a MAJOR OEM, and he announces “Here to speak about Head-in-pillow, is our Application Engineer, Mario…” Let’s talk about SURPRISE.
Well, my torture is your benefit…
Head-in-pillow is the incomplete wetting of the entire solder joint or a Ball-Grid Array (BGA) or Chip-Scale Package (CSP), or even a Package-On-Package (PoP). From cross-sections, it actually looks like a head has pressed into a soft pillow.
Two issues, poor wetting and component warpage cause head-in-pillow defects. They both look the same, but you can identify them because random head-in-pillow defects are from poor wetting and edge or center defects are from warpage.
I have separated all the head-in-pillow defect types into three areas. These are Supply Issues, Process Issues and Material Issues. They can be defined like this:
Supply issues are everything before you put them on the line. This includes oxidation, or any other oxidation/hydroxide effects.
Process Issues are everything that is on-line. Including printing, placement and reflow.
Material Issues is everything that has to do with the soldering itself, such as wetting capacity or flux exhaustion.
I will go in depth with each one of these issues in further posts.
More information may be found at Online Help: Indium Knowledge Base.