Actually this is not uncommon; the point is that whether is it too large? Concentrate on fine pitch components, and determine whether the post reflow solder joints result is acceptable or not. I believed that you will not face any issue due to this "problem". But if you use, Solder paste inspection machine (inspection on stencil or on the deposited paste on PCB) you will have to "wait" await to minimise rejects. What is the flux % which you asked for? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven Sent: Thursday, 31 July 2008 5:46 PM To: [log in to unmask] Subject: Re: [TN] Solder Paste with craters. Leif, You have received so many great suggestions thus far that I feel somewhat silly asking this, but ... You are using a metal squeegee, correct ... !? I will go back to my corner now... Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey Sent: Wednesday, July 30, 2008 12:31 PM To: [log in to unmask] Subject: Re: [TN] Solder Paste with craters. I have not see that kind of print anomaly. Obviously this will change the solder volume and it is undesirable. While the craters are not causing the fines. They could be symptomatic of a failure in the material that results in fines. The flux should dry and then the solder coalesce onto the feature at reflow. Some pastes fail in so that the flux runs all over carrying the solder spheres with it off the pads. Then at reflow the flux burns off leaving fines stranded everywhere. I have run into this problem and I have receive bad solder paste from reputable suppliers that do this fresh from a sealed jar. You could observe this with a BGA rework station, hot air or IR pen. Compare the problem paste with fresh paste and paste that does not produce fines. I think you will see a difference. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Wednesday, July 30, 2008 11:59 AM To: [log in to unmask] Subject: Re: [TN] Solder Paste with craters. Hi Leif! I have your pictures posted. Go to: http://stevezeva.homestead.com/files/air_bubbles_and_craters_1.jpg http://stevezeva.homestead.com/files/air_bubbles_and_craters_2.jpg Is the percentage of metals the same as your leaded paste? I also think the rheology the paste won't be the same with as it is with the leaded paste, so there will most likely have to be changes with the set-up of the print. It almost looks like the separation speed is too fast, and the paste isn't given time to pull away from the inside of the apertures causing the crater... Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum Sent: Wednesday, July 30, 2008 8:29 AM To: [log in to unmask] Subject: [TN] Solder Paste with craters. Technetters, We are having an issue with solder fines on our lead free boards. We are using SAC305 WS and no nitrogen. I noticed that our boards have craters in the paste on the pads after being printed. Not all pads are deposited this way, but maybe 25%. These craters have an air bubble in them. The bubbles usually burst before the boards goes into the P&P, but the crater stays. The screening process is exactly the same for leaded and unleaded paste. The leaded paste does not behave this way. Could these craters be a symptom of the cause of the solder fines? Anyone have any experience with this? How do I go about posting pictures to stevezeva.homestead.com?. -- Leif Erik Laerum Quality Assurance Manager Texas Memory Systems [log in to unmask] Tel: (713) 266-3200 x468 www.texmemsys.com --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 ----------------------------------------------------- THE INFORMATION CONTAINED IN THIS E-MAIL MESSAGE AND ANY ATTACHMENTS SENT FROM GENTEX CORPORATION IS GENTEX CONFIDENTIAL INFORMATION INTENDED ONLY FOR THE PERSONAL USE OF THE INDIVIDUAL OR ENTITY NAMED ABOVE. If you are not the intended recipient, you are hereby notified that any review, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by return e-mail, and delete this e-mail message and any attachments from your computer. [gntx v.1] --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 -----------------------------------------------------