Steve, I understand what you are saying, but Peter spoke specifically about a possible alloy effect and I was trying to get some more info about that. Bev -----Original Message----- From: Creswick, Steven [mailto:[log in to unmask]] Sent: April 10, 2002 12:21 PM To: [log in to unmask] Subject: Re: [TN] 0402 tombstone problem Could it be that rather than Sn/Pb composition, it might be related to the wettability (prior storage conditions) of the components in question - thereby tying it into the required activity level of the flux? Considered rectangular pads with rounded corners, or 'rectangular' pads with semi-circular ends? It has worked on LTCC based product. Steven Creswick - Gentex.Corp -----Original Message----- From: Bev Christian [mailto:[log in to unmask]] Sent: Wednesday, April 10, 2002 8:46 AM To: [log in to unmask] Subject: Re: [TN] 0402 tombstone problem Peter, So which is worse - high tin (e.g. Sn/Pb95/5) or relatively "high" lead (Sn/Pb63/37)? Bev Christian Research in Motion -----Original Message----- From: Peter Lee [mailto:[log in to unmask]] Sent: April 10, 2002 12:07 AM To: [log in to unmask] Subject: Re: [TN] 0402 tombstone problem Our experience with eliminating 0402 tombstoning was to try different no-clean solder paste. We've also found that the parts' end termination tin/lead % has some negative impact on the yield. Rgds, Peter -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: April 9, 2002 8:13 PM To: [log in to unmask] Subject: Re: [TN] 0402 tombstone problem I just heard something not too long ago, that round pads for 0402's are the way to go. Never heard of that before, but just recently received a board for quote that uses round pads for the 0402 components...anybody else ever heard of this? Guess I'll find out how it works inna little while, while pondering why a round pad would work better than a square pad.... -Steve Gregory- Edward, When we do everything correct on 0402 and 0201 and still have components standing-up, we often look to the component terminations and find poor plating. Good luck Dave Fish ----- Original Message ----- From: "Edward S. Wheeler" <[log in to unmask]> To: <[log in to unmask]> Sent: Tuesday, April 09, 2002 10:59 AM Subject: [TN] 0402 tombstone problem > Hi folks, we are running a new board with 0402 parts on it. It seems that > we are having a tombstone problem as well as a problem with parts not > staying centered on the pads. We are currently using 20 mil square pads on > the board, with 20 mils of spacing between them. Our stencil is 6 mils > thick, laser cut and electro polished. The trapezoidal walled apertures are > slightly reduced, 17 mils square, and centered on the pads. It appears the > chip shooter is placing the parts perfectly. We are using eutectic solder > paste with an OA flux, and reflowing the parts using the recommended profile. > > Are there any suggestions any of you might have concerning this size of a > part? Is there a better stencil design, reflow profile, or pad design that > could help us out? I would appreciate any suggestions. > > Thanks. > > Ed