Interesting feedback. The stencil is indeed 6 mil thick. The resistor pack pads are 22 x 10 mil and have 20 mil pitch. The smallest BGA pads are 20 mil and have 30 mil pitch. Is it the case that type 5 has a higher flux percentage than the type 3. If so that could explain some of our findings. Leif Erik Laerum Quality Assurance Manager Texas Memory Systems [log in to unmask] Tel: (713) 266-3200 x468 www.texmemsys.com Guy Ramsey wrote: > 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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