Hi Jim, are you describing the ubiquitous 'mid-chip ball' or 'squeeze ball'? If so, I worked on this when I was developing solder paste. My take on it is, it is caused too much paste followed by paste slump, cold slump would exacerbate the issue, but hot slump will cause the paste (paste flux) to 'flow' out before reflow occurs and the surface tension of the metal becomes dominant. Either change your paste to one that doesn't cold slump or hot slump, they exist through careful selection and careful incorporation of appropriate solvents or spend time modifying your reflow profile to dry the paste faster at the start of the profile and reduce the flow characteristics at higher temperatures. It's also worth considering re-designing the stencil to reduce the paste printed in the culprit areas. If you want to carry out some tests, find a hot-stage microscope and run some pastes at different profiles, you'll be able to see the flow-out and other interesting phenomenon. With a modern system you'll be able to programme real time profiles and record the data and video on a PC. For what it's worth, Andrew Hoggan BBA Associates Ltd www.bba-associates.com -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Marsico, James Sent: 14 August 2001 20:34 To: [log in to unmask] Subject: [TN] 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 ---------------------------------------------------------------------------------