Smallest pads under mm BGA + 6 (60 mil??)laser cut stencil + type 5 paste = me confused. This would be, in my opinion, a recipe for hot slump and solder fines. A design with components and features like you describe should be fine with type 3 paste. Let's talk about those capacitor and resistor networks. What is their pitch and land pattern dimension? Smaller than the BGA? A lot smaller? Okay maybe type 4 paste and a 4 or 5 mil stencil. Guy -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum Sent: Thursday, July 31, 2008 11:34 AM To: [log in to unmask] Subject: Re: [TN] Solder Paste with craters. Paul et al, The bubbles are more prevalent on the smallest apertures such as 1 mm BGA pads and the resistor/capacitor pack pads. The temperature in the production area is between 68F and 75F. Humidity is relatively steady at 40%. (We are in Houston....) If anyone has any suggestions how to test the screens for cleanliness that would be great. That is a part of our process we do not control. We have a stencil cleaner, but we can only visually see if they are really getting clean. We also bought some stencil cleaner for manually wiping down a screen, but it actually makes the screens "greasy". We stopped using it. Ours stencils are the standard 60 mil laser cut. We do use a metal squeegee. Leif Erik Laerum Quality Assurance Manager Texas Memory Systems [log in to unmask] Tel: (713) 266-3200 x468 www.texmemsys.com Paul Edwards wrote: > Leif, > > I just have 2 questions... > > What size apertures do these bubbles occur on and is there a > particular aperture orientation in which they are prevalent? > > What is the humidity and temperature of the environment for the paste > prior to putting it on the stencil>> > > Have seen something similar in certain kinds of SAC W/S pastes that > have been exposed to too much moisture and certain stencil cleaning > compounds...The saponifier was making soap bubbles when rolling in the > paste... > > Paul > Paul Edwards > Surface Art Engineering > > > > > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum > Sent: Wednesday, July 30, 2008 1:56 PM > To: [log in to unmask] > Subject: Re: [TN] Solder Paste with craters. > > Thank you everyone for contributing. Especially you, Richard. > > First of all these are NOT via in cap boards and we are using FR4. > Been there done that.... > > Most of the items brought up by Richard we do have established > processes for. These are according to the recommendations of the > solder vendor, but if others feel differently, please chime in. > We log the solder used for each batch and the Date of Manufacture > for this. We typically do not accept a batch of solder that is older > than 3 mts. This is so that we do not end up with too much out of date > solder at the end. > > - Solder is brought out of the fridge minimum 12 hours before use. > - We set a time limit that solder must can be stored out of the fridge > a maximum of 3 mts. Practically this ends up around 1 month max. > - We do reuse solder that has been on the screen for up to two weeks. > Then we throw it out. > - We never put solder back in the fridge. > - We are evaluating new suppliers of solder at the moment. We have not > audited the currents supplier, but that is a good idea. We always get > the solder couriered locally and in a cool container so I do not have > any evidence that would lead me to put this on the solder vendor, > but..... > - As our process works boards sit no longer than 1 hour with solder. > Usually much shorter than that. > - We are using Type 5 solder actually. > - All misprints go though the wash before it is reprinted. > - We use a DEK 248 that is not as automatic as I would like and some > of the issues we see are due to this repeatability problem, but from > the data I have gathered, this is not the cause of the solder fines > and craters. > - A Solder AOI would be nice. We do not have one of these (yet???) > - There could be an issue with too much solder. We are going to reduce > apertures some. There is some evidence of excessive solder. > - I am going to experiment with slowing down the print separation speed. > Good point. > > Thx. > > Leif Erik Laerum > Quality Assurance Manager > Texas Memory Systems > [log in to unmask] > Tel: (713) 266-3200 x468 > www.texmemsys.com <http://www.texmemsys.com> > > > > Inge wrote: > > Hi Leif, you've just listened to His Master's Voice. > > You should take off your cap, when you speak to Richard Stadem. > > Impressive! I begin to feel that there are two exceptional stars at TN. > > Steve...we already knew > > Richard...a supernova > > > > Inge > > > > Gah...my example was not very clever...a supernova is bright just > > for a short time...hmmm...a red giant then? hmmm...or a white > > dwarf...hm...none of them very striking....hmm....shining like > > Betelgeuse...hmm.....maybe Master Whittaker can give a hand? > > > > > > ----- Original Message ----- From: "Stadem, Richard D." > > <[log in to unmask]> > > To: <[log in to unmask]> > > Sent: Wednesday, July 30, 2008 6:53 AM > > Subject: Re: [TN] Solder Paste with craters. > > > > > > Hi, Leif > > Send your pictures to [log in to unmask] > > > > Can you tell me what solder paste it is you are using? How was it > > qualified for use? > > > > Here are just some of the questions you need to ask yourself in > > order to determine why you have an issue with solder fines: > > Do you have a good documented solder paste handling procedure? How > > is the paste handled, from vendor or distributor to your factory? > > When was the last time you stopped in at the distributor to verify > > their stock is being rotated and is kept refrigerated immediately > > upon receipt from the factory? How often do they turn the packages > > upside down to prevent flux separation? Are they a certified > > distributor who will pass on to you a lot recall notice from your > > solder paste vendor if there is a known bad lot? > > How long is the paste allowed to sit out on the stencil and how many > > times can a line of paste on the stencil be sheared (printed back > > and > > forth) before it is removed and replenished with fresh paste? Are > > the operators allowed to scrape up the unused paste on the stencil > > and re-deposit it into a jar for re-use later? Is the jar or tube of > > solder paste, once removed from refrigeration, allowed to set for > > two to four hours (depending on paste vendor and paste type) to > > reach room temperature prior to printing? Once removed from the > > refrigerator, is unused solder paste allowed to be put back in the > > refrigerator? Are you using Type 4 paste or Type 3? How good is the > > printer setup, ie, the repeatability of the registration of the > > stencil to the PWB? Are you performing some type of aperture > > reduction on all pads in general and at least a 50% reduction on > > large belly pads to prevent solder fines from being printed onto the > > board? If a board is misprinted, does the operator know better than > > to simply wipe off the board (embedding the paste into every space > > between the edges of the pads and the soldermask, into every small > > via, into every through hole, etc.) but is there a documented > > procedure detailing how the misprinted board is to be cleaned to > > prevent this? How is the solder paste packaged, jar or tube? (Tubes > > prevent a much larger volume of paste from being exposed to air and > > humidity, and also help prevent re-use of solder paste that has been > > out for awhile). Do you perform a good solder paste print inspection > > using a 3d AOI or some other type of automated inspection, and do > > you use the data from this inspection process to detect (real-time) paste defect trends and react to them with corrective actions? > > > > Sorry to ask so many questions, but all of these can contribute to > > fines, and there are many more factors that can cause them. > > > > > > > > -----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 <http://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 > > ----------------------------------------------------- > > --------------------------------------------------- > 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 > ----------------------------------------------------- > ---------------------------------------------------------------------- > -- > ** > > This email and any attachments thereto may contain private, > confidential, and privileged material for the sole use of the intended > recipient. 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