Ofer, Have seen this before on parts with bad lead plating... What we had was trapped moisture or volatiles in the part metallization layers under the solder plating... What is interesting is that your seems to only happens on pasted pads...... It could be that the plating is porous enough to allow the volatiles in the paste wick up through it and bubble up the Sn plating at the hot side of the part... Paul Paul Edwards Process Engineering [log in to unmask] Tel: 408-433-4700 FAX: 408-433-9988 Surface Art Engineering 81Bonaventura Dr. San Jose, CA 95134 DUNS: 944740570 CAGE/NCAGE: 1XZ48 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Ofer Cohen Sent: Monday, September 12, 2005 12:06 PM To: [log in to unmask] Subject: Re: [TN] Resistor Acne Phil, The resistor termination is pure Sn, and it is soldered using Sn62Pb38Ag2. I sent some resistors on a blank PCB to the reflow oven. I placed paste on some of the terminations. The bubbles appeared on those termination where paste was present. Regards Ofer Cohen Manager Quality Assurance, Reliability and Production Technologies Seabridge Ltd. - A Siemens Company Siemens COM FN A SB -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro Sent: Monday, September 12, 2005 19:44 To: [log in to unmask] Subject: Re: [TN] Resistor Acne Hi Ofer, What is the metalization of the resistor termination and what alloy solderpaste are you using with it? Have you watched it under a rework reflow to see if it bubbles? A microsection would be helpful to know what is going on beneath the surface. Phil Ofer Cohen <[log in to unmask]> wrote: Hello, all, An inspector found something that Steve Gregory named as "resistor acne" (all rights reserved to Steve). We were not able to figure out the possible causes and effect on the product reliability. Steve placed the picture on his site. Please go to http://www.stevezeva.homestead.com click on "Picture Page 2", then Look for "Resistor Acne"... Any idea will be welcomed. Regards Ofer Cohen Manager Quality Assurance, Reliability and Production Technologies Seabridge Ltd. - A Siemens Company Siemens COM FN A SB --------------------------------------------------- Technet Mail List provided as a 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 847-615-7100 ext.2815 ----------------------------------------------------- __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! 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