Gene: You left out something: "We have just received a batch of boards from the assembly shop which have cracked ___________when the connectors were inserted." Fill in the space... Describe in detail, what you are seeing../happening Does the board have Ni/gold for the finish ontop of the complete board including the press fit holes? Bob Z > -----Original Message----- > From: Gene Holmes [SMTP:[log in to unmask]] > Sent: Thursday, September 02, 1999 6:35 PM > To: [log in to unmask] > Subject: [TN] Cracking PCB's > > Sorry to dump such a long list on you all at the end of the week, but I'm > kinda desperate for some answers. > I know some of these questions have been asked before, so I apologise if I > am revisiting old ground here. > Over the past few months we have had a series of boards made which have a > variety of BGAs and fine pitch devices on them as well as press fit > backplane connectors. The boards are 1.6mm FR4 with an immersion gold > finish to get the required flatness for the BGAs and fine pitch > components, > the connectors are from ERNI. > We have just received a batch of boards from the assembly shop which have > cracked when the connectors were inserted. This is really bad news as > these > babies cost in excess of 4000 dollars each. This has prompted an inquiry > which has raised more questions than I can answer confidently.There are a > lot of questions that I need both the fab and assembly houses who carried > out the work to answer in due course. In the meantime I'm hoping you guys > can dump a little of your vast knowledge on me - sorry for the long list. > Here goes... > 1. The spec sheet for the connectors call for a drill of 0.007in with a > finished size of 0.006in Does the use of gold mean a thinner finish and > perhaps the fab shop are drilling smaller to accommodate this and > subsequently cause the pin of the connector to try and cut through the > board material rather than swage through the metal ? > > 2.As the gold finish is harder than tin lead would this cause insertion > forces to increase to the extent that the board could crack? > > 3.This is one for the assemblers out there. Do you measure the insertion > force when fitting press fit devices? > > 4.Not wanting to forget the chemists. The material the fab house is using > has an Er of 3.8 does this mean more epoxy less glass and possibly more > prone to cracking. > > 5.What finish are other people specifying for this kind of assembly? > > 6.Finally,I have also heard of possible reliability issues when press fit > connectors are combined with gold finish. What they, if any, and how do I > deal with them. > > Sorry once again for the long list, but it's kinda worrying, sitting here > looking at a potential 20000 dollar pile of scrap.. oh happy days > > Cheers > Gene > > > Gene Holmes > HCD Ltd > www.hcduk.com > > ############################################################## > TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for > additional > information. > If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or > 847-509-9700 ext.5365 > ############################################################## ############################################################## TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################