With OPAMP CSPs of the same size we have adopted the manufacturer's (Maxim) recommendation for an asymmetrical opening in the stencil. http://pdfserv.maxim-ic.com/en/an/AN1891.pdf http://pdfserv.maxim-ic.com/en/an/AN3377.pdf also recommends a corresponding opening in the solder mask. It looks something like this and works for us. ___ ___ ___ ! ! ! ! ! ! ! ! ! ! ! ! ! O! ! O ! !O ! --- --- --- ___ ___ ___ ! ! ! ! ! ! ! O! ! O ! !O ! ! ! ! ! ! ! --- --- --- ___ ___ ___ ! O! ! O ! !O ! ! ! ! ! ! ! ! ! ! ! ! ! --- --- --- Volkmar Volkmar Huss, C.I.D. ----------------------------- PRETTL ELEKTRONIK Luebeck GmbH -----Original Message----- From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Susy Webb Sent: Monday, November 06, 2006 6:24 PM To: [log in to unmask] Subject: [DC] .5 mm pitch BGA Hi all, We are designing a 9 pin BGA into a board and having some board issues. The pitch of the part is .5mm and the part is a fet (higher power needs). The data sheet recommends a .25mm (.010 mil) pad which we have done, but we are having problems with the part twisting a bit on placement (requiring rework after reflow). After the initial board build, we adapted a thinner solder paste and tied the pads on opposite sides of the part (R & L) to vias to add some extra pull to keep the device in place. That build was better, but still not as accurate as we would like because of the solder mask opening size (+.004 overall) and SM placement tolerance is so huge compared to pad size... only .010. SO..... my question is.... Are any others using .5 mm pitch BGAs, and if so, what are you doing to make them assemble properly. Thanks, Susy ------------------------------------------------------------------------ --------- DesignerCouncil 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 DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ------------------------------------------------------------------------ --------- --------------------------------------------------------------------------------- DesignerCouncil 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 DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------------