Hello Todd, I agree with the response on smaller corner balls may be due to warpage of the PBGA substrate. The 45% voids in your solder balls need to be verified with a cross section. I thought I was seeing 35% voids and found through cross sectioning that they were really a number of smaller voids which the x-ray could not resolve. Jim Kittel > -----Original Message----- > From: Todd Ness [SMTP:[log in to unmask]] > Sent: Friday, April 23, 1999 9:56 AM > To: [log in to unmask] > Subject: [TN] BGA Voiding Problem > > We are just starting to manufacture a PCB with a .039" fine-line PBGA. > We are currently seeing voids, mainly in the center, that are as much > as 45%. We also intermittently see the corner balls of the PBGA > smaller than the center balls. We are using a 6-mil stencil with a 1:1 > aperture size (.019" mil). We are using a convection oven and > reflowing in air. The solder paste is an OA 62SN36PB02AG and the > reflow profile is: > Preheat - 0-150 degrees C in 90 sec > Soak - 150-189 degrees C for 120 sec > Reflow - 189-210 degrees C for 60 sec > Thermocouples were attached to both the corner and center of the PBGA > and they both had the exact same profile with a max temp of 210 > Degrees C. > > Does anyone have any recommendations for minimizing the amount of > voiding? Is 45% voiding acceptable? What would explain the corner > balls being smaller than the center balls? > > Thank you for your input. > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with > following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line Services" > section for additional information. > For technical support contact Hugo Scaramuzza at [log in to unmask] or > 847-509-9700 ext.312 > ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################