The adhesive was printed and cured at no more than 2deg/s and 150degC for 100secs. The particular adhesive used was Epibond 7275. We suspected that it was a material related issue - either the glue was mishandled and left too long on the line, or old/ expired batch of glue was used. Any suggestion on method to drive the moisture away under the components? Baking conditions? Rgds, Peter >Date: Mon, 25 Aug 2003 07:47:30 -0400 >Reply-To: [log in to unmask] >Sender: TechNet <[log in to unmask]> >From: joyce <[log in to unmask]> >Organization: EXFO-TO >Subject: Re: Moisture under chip capacitors >X-To: "TechNet E-Mail Forum." <[log in to unmask]>, Peter Lee <[log in to unmask]> >In-Reply-To: <000001c36abe$e03472d0$7e63ad8e@homeg8br34o791> >Content-Type: text/plain; charset="iso-8859-1" >What is the adhesive and how was it cured? jk >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Lee >Sent: Monday, August 25, 2003 12:11 AM >To: [log in to unmask] >Subject: [TN] Moisture under chip capacitors > > >Technet, > >I have come across a rash of failed assemblies that have 0805 >capacitors and resistors, bottom side glued, wave soldered and >washed. Trouble shooter reported touching up the solder joints >on a few areas and the boards would pass test. > >I had a look at one board which was reported to have a 0805 >56K resistor with "drifting" values. I pulled the component >off mechanically in order not to apply any heat and noticed >several mini-voids within the adhesive body. I have seen >solder bridge within the glue before but this was the first >time I saw wet residue within the voids. > >You can view a sample image from Steve's web site: >http://www.stevezeva.homestead.com/files/SMTAdhesive.jpg > >The >image showed the bottom side of the cracked resistor after >removal (white), with a portion of solder mask (green) and SMT >adhesive (red). > >I used a 8mil stencil. The thermal profile was verified and >conformed to the slope/ curing specs. > >Has anyone seen this before? Any explanation as to how the >void was formed and how moisture got tapped in? Does anyone >re-use their glue on the line or throw away any left-over to >avoid moisture in the glue? > > > >Rgds, >Peter > >--------------------------------------------------- >Technet Mail List provided as a free service by IPC using >LISTSERV 1.8e 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 or >(re-start) delivery of Technet send e-mail to >[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE >mailing per day of all the posts: send e-mail to >[log in to unmask]: SET Technet Digest Search the archives of >previous posts at: http://listserv.ipc.org/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 847-509-9700 ext.5315 >----------------------------------------------------- > --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 847-509-9700 ext.5315 -----------------------------------------------------