Head-in-pillow defects caused by everything before the components go on-line can be grouped into Supply Issues. Some specific issues within this group are oxidation, hydroxidation and silver segregation. Oxidation is the most known. This is where during the manufacture, packaging, shipment or storage of the bumped components, these bumps have formed a hard-to-solder oxide coating on their surface. This is wrongly called "Black Ball" because the surface oxidation coating is not always dark, and on the flip side, dark sphere are almost always not hard-to-solder. Poor air introduced into the manufacturing, un-sealed packaging or in the storage of the components contributes to this surface oxidation. Hydroxidation, a little less well known, is when a surface hydroxide is formed, but is usually limited to the manufacturing process as it is commonly caused by the molten spheres exposed to higher humidity. Hydroxidation is extremely hard-to-solder. Another issue that we have seen at customers is called "silver segregation". At this particular customer, the head-in-pillow was such a problem, that the components were sent for analysis, and the soldering surface of the sphere was found to be 36% silver. The actual causes of the silver segregation have still a mystery to me, but my thoughts are leaning towards the manufacturing of the sphere, particularly the cooling rate. The attached picture is actually of that issue, where a "silver tail" has formed on the sphere, much like a tin whisker. Supply type head-in-pillow defects are something that we look for when addressing customers, but are usually outside Indium's sphere of influence. (Pun intended, ha!) More information may be found at Online Help: Indium Knowledge Base.