I assume the automated inspection machines (which brand are they, by the way?) are finding your printing defects, some of which you described. When they spit out the defect list, a skilled operator should be able to rework (efficiently) any small, isolated defects prior to sending the PWB to pick and place. Defects such as a single pad with insufficient solder, one or two paste bridges due to slumping, etc., are examples of this. Application of a small amount of solder paste by pin transfer with a small dental pick and/or running the pick between two slumped deposits to separate them can be done. For wholesale misregistration or more than two or three defects per board, they should be cleaned and re-printed. I understand why the requirement is there that does not allow wiping or cleaning of the PWB, as dry wiping and attempting to reprint results in pwbs with solder paste particles (called solder fines) embedded into vias, in spaces between the pads and the solder mask, and other places you do not want solder to be. However, that does not mean that the misprinted PWBs should be handled as scrap. If you have a stencil washer, the misprinted PWBs should be able to be placed in that and cleaned, followed by a pass through the assembly wash machine, baked for 1/2 hour to remove all surface moisture, inspected under at least 10X magnification, and put back into the cue at the beginning of the process. This cleaning without any wiping will remove all solder paste on almost any PWB. However, if the stencil registration is grossly off, the squeegee will press solder paste fines in the areas we just discussed, and once impressed it is nearly impossible to remove them. It should be noted that small fines attached along the sides of pads or trapped under components is acceptable as a process indicator condition, even for Class 3 product per J-STD-001. Of course, this is dependent on the internal requirements of the OEM as determined by the end-use requirements. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall Sent: Wednesday, January 21, 2009 9:57 AM To: [log in to unmask] Subject: [TN] Automated Solder Paste Inspection - Best Practices Request Technetters, I sent this out last week during a period of nasty weather across the country, and of course, got limited responses. I'm trying it again, as this is quite important. Please help me if you can. Thanks! Leland -----Original Message----- From: Leland Woodall Sent: Thursday, January 15, 2009 2:40 PM To: 'TechNet E-Mail Forum' Subject: Automated Solder Paste Inspection - Best Practices Request Everyone, We have automated solder paste inspection machines immediately following each of our screen printers. These all check for volume, height, and pad coverage. We run only lead-free products, and also have a requirement that disallows any wiping or cleaning of a misprinted board. I'm looking for folks running a similar operation that can give me some recommendations on how they manage this process. How many bridges do you allow? How do you handle insufficients or inadequate pad coverage? Insufficient paste volume bothers me, as I'm always afraid our post-reflow AOI process will not detect the condition. I also hate to scrap a board that has only a couple of pads with low or no solder. Any suggestions on how we can minimize scrap but ensure we have no escapes? Do we write down the effected pads, mark the board, place the parts, and capture it after the oven? How could one reliably manage this? Your comments are sincerely appreciated. Stay warm! Leland Woodall --------------------------------------------------- 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 -----------------------------------------------------