Hi Dave, A shrinkage void in an ingot occurs where it solidifies last---in its center. The same is true for SJs, except that they do not necessarily cool from the outside in. but a connected to various heatsinks and reservoirs---the component is typically a heat sink [coolest] and the PCB is a reservoir [hottest], with various heat transfer conditions on the surface due to forced air/N2. Overall, SJs tend to solidify first at their surface; hence, most shrinkage voids are to be found there. Werner -----Original Message----- From: David D. Hillman <[log in to unmask]> To: [log in to unmask] Sent: Tue, Apr 20, 2010 10:13 am Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls Hi Bev - in theory, a shrinkage void in a solderball is the same physics as a shrinkage void in a aluminum or steel casting so no, the shrinkage void would not have to necessarily always reach a surface. However, after looking at several hundred SAC BGA/CSP cross-sections, I have nearly always (99.999%) found a path of a shrinkage void to the solderball surface. Because we have a very limited and very small molten solder "volume", I think you will find a surface connection. And I guess I'll bite - why the question? Dave Hillman Rockwell Collins [log in to unmask] Bev Christian <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/20/2010 08:16 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Bev Christian <[log in to unmask]> To [log in to unmask] cc Subject [TN] SAC Shrinkage Voids in BGA Balls TechNetters, Do all SAC shrinkage voids in BGA balls reach/start at the surface of the ball? I realize I may be stumped by a 2D cross-section of a 3D phenomenon, but I thought I would ask this august body. 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