I like Loan's answer because solderballs normally form in the middle along the side of the chip component and not underneath. The normal solderball is formed when solder follows the flux under the component during reflow then is "squeezed" out to the side when the molten solder solidifies, shrinks and pulls the chip flush to the board surface. I could see the pulling down action stopped by, say, epoxy or soldermask non-existence or over presence. Are these balls being formed during SMD or solderwave do you think? An aqueous SMT paste process usually will wash this ball away. No-clean paste requires not forming them in the first place (and only allowing them to stay if they are imbedded in flux and less than a certain size, etc.) by controlling stencil aperature, solder printing(x-y and z(volume)), solder choice and oven profile. Is this an aqueous or no-clean solder paste/process we are talking about? Dorothy Lush Manufacturing Engineer > ---------- > From: Marsico, James[SMTP:[log in to unmask]] > Reply To: TechNet E-Mail Forum.;Marsico, James > Sent: Tuesday, August 14, 2001 12:34 PM > To: [log in to unmask] > Subject: soldr balls > > Here's a relatively basic SMT question, but we've haven't experienced this > before. We're seeing solder balls under (way under, in the center) chip > components. Any recommendations? > > Jim Marsico > Senior Engineer > Production Engineering > EDO Electronics Systems Group > [log in to unmask] <mailto:[log in to unmask]> > 631-595-5879 > > -------------------------------------------------------------------------- > ------- > 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 > -------------------------------------------------------------------------- > ------- > --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------