Hi, Mike, How are you masking the stencil? From the top or the bottom? Too thick a mask, especially on the bottom, will cause the stencil to deform and you'll lose the gasketing of the stencil to the board. For low volume, the simplest form of masking that works is Kapton tape on the top side. It's thin and strong enough, and doesn't cause additional wear to the stencil. If you paste a very fine pitch location but don't place a component, there are no leads to "soak up" the solder when it melts. Particularly if the pads are over-pasted (width), there is a greater tendency for bridging to occur. If you have excessive stencil wear, then you're probably looking at replacing the stencil soon anyway, so either consider omitting the QFP pattern next time or reducing the aperture size. Peter Duncan Michael Bell <Michael.Bell@ To: [log in to unmask] GPC.CO.NZ> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Sent by: Aero/ST Group) TechNet Subject: [TN] QFP Solder Pad Shorts <[log in to unmask] RG> 11/07/01 07:13 PM Please respond to "TechNet E-Mail Forum." Hi all, I have just come across a problem with a reflowed PCB that has a footprint for a QFP on it, but no QFP placed. It seems the footprint has paste stenciled onto it, various other components placed, and then reflowed. However, after reflow, it is notorious for having a number of solder shorts. We have tried masking off the apetures in the stencil to avoid depositing paste on the pads, but I am noticing wear on the stencil. Has anyone got any ideas of what is causing the solder shorts between the pads, or how to solve this??? Cheers Mike --------------------------------------------------------------------------------- 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 To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL 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 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------------------------------------- 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 To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------------