I guess pictures would be in order. Verbally, it seems your paste is wetting as required to the pads but what's with the "mounds?" The solder balls are deforming but "smershing" down into the COMPLETELY melted solder paste as if displacing it. So, what's wrong with the missing picture? Why are the solder balls incapable of wetting? Contamination? Oxidation? Wrong alloy? I see your HASL finish as acceptable and wetting normally. What's with the tinned and fused finish. Is it really tin/lead plated and fused? Anyway, besides the possibility of the solder balls being incapable of solder wetting, what is the recommended solder paste profile and how close are you to it - really? And, again, the corner balls will be hotter causing them, most often, to collapse first though this is dependent upon the rest collapsing or a non-parallel device to substrate condition will exist and will be easily seen - leaving the rest to follow, including the ones internal to the device and array pattern. In other words, the corner balls will "melt" first but will not collapse until all others do the same depending on number. Earl Moon --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------