I've seen that tomb-stoning problem with 0402 components once. It was caused by a huge soldermask-to-copper Layer offset in PCB production, due to this offset, there was soldermask on the pad. Since the offset was violating IPC spec, we've sent the whole batch back to the PCB vendor. I've never seen this type of problems with quality PCBs. Mit freundlichen Grüßen / Kind regards. Gert Havermann Signal Integrity Engineer >SI & CAE >HARTING Electronics GmbH & Co. KG >Marienwerderstraße 3 >D-32339 Espelkamp > >Phone +49 5772 47 857 >Fax +49 5772 47 179 >mailto:gert.havermann@xxxxxxxxxxx >http://www.HARTING.com > -------------------------------------------------------------------------- Absender ist HARTING Electronics GmbH & Co. KG; Sitz der Gesellschaft: Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596; persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH; Sitz der Komplementär-GmbH: Espelkamp; Registergericht der Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH: HRB 8808; Geschäftsführer: Torsten Ratzmann -----Ursprüngliche Nachricht----- Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im Auftrag von Thompson, Gary D (Gary) Gesendet: Mittwoch, 7. Januar 2009 18:14 An: si-list Betreff: [SI-LIST] Manufacturing Issues Sorry for the somewhat off-topic nature of these questions. Hopefully someone here can steer me in the right direction. I've recently receive a manufacturability review report from a top tier contract manufacturer, wherein they made some recommendations that I'm not too comfortable with. Part of me says "they're the experts," and I should accept their input. The other part wants to sanity check these suggestions just to make sure I'm not running down a single-source rat hole :^) Suggestion 1 We're using more and more QFN type packages that have a thermal ground pad in the middle. Typically, we've just spaced vias in a grid on this pad down to internal ground layers. The CM says too much solder gets wicked down the vias leaving the pad too dry. They recommend we 1) move the vias to the outside edges of the pad and 2) cover them or dam them with soldermask to prevent solder from flowing that direction. Seems to me most manufacturer-recommended footprints I've seen do it the way we do, not the way the report recommended. Suggestion 2 This report claimed soldermask between pads on 0603 and 0402 discretes left a bump between the pads that promoted tomb-stoning. They recommend removal of soldermask between these pads. I've never seen this done before, and the CM was not able to actually quantify the failure rates due to this soldermask. The last thing we want, though, is a solder bridge under an 0402 part... Anybody else out there heard of this stuff or have recommendations on a more fitting place to ask these questions? Thanks. ============================================================== Gary Thompson Phone: (512) 821-6521 Systems/Applications Engineering FAX: (512) 821-6810 LSI Corp. Mobile: (512) 751-8115 Network and Storage Products Email: gary.thompson@xxxxxxx ==============================================================------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu