Not sooooo All you need is a good laser interferometer, a sense of humor and plenty of time........ Although you are close Dewey - the first reference I have ever found is Isaiah 41 vs 7: which says and I quote: " It is ready for the soldering" John Burke (408) 515 4992 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE) Sent: Thursday, July 31, 2008 2:30 PM To: [log in to unmask] Subject: Re: [TN] Solder Paste with craters. Yeah, but those clay tablets and papyrus reeds are hard to scan. Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Sent: Thursday, July 31, 2008 2:27 PM To: [log in to unmask] Subject: Re: [TN] Solder Paste with craters. Mike is too young, and he is english.............. ???????????? You didn't know? Most reports, as far as I remember, were american. IBM, ESL, HERAUS, duPONT, Honeywell, etc Inge ----- Original Message ----- From: "John Burke" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, July 31, 2008 2:14 PM Subject: Re: [TN] Solder Paste with craters. > If you want REALLY old papers on Rheology Mike Fenner will have/remember > them - sorry Mike!!...........NOT > > > > John Burke > > (408) 515 4992 > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge > Sent: Thursday, July 31, 2008 1:52 PM > To: [log in to unmask] > Subject: Re: [TN] Solder Paste with craters. > > Leif Erik, > > seems as the focus is now on the stencil. Good, because this may be the > red > thread. Imagine the squeege has just passed and the extremly small laser > cut > > holes are filled with your paste. Next, the stencil is ready to separate > from the board. What happens? I guess the rather rough metal walls are > little unwilling to let go the paste, while the paste has already > established a grip on the ENIG pad through surface wetting and adhesion > forces. The later one wins over the adhesion from the stencil walls > (otherwise, there had been no prints). However, the adhesion from the > walls > will expand or elongate the paste body for fractions of a second. But the > true volume is constant still, isn't it. Then a compensation must be done, > namely, the middle of the paste body must sink. You get a small , what > shall > > I call it, a inward bend instead of a flat paste surface. When the the > stencil wall adhesion is overcome, the paste glides backward and leaves > the > stencil, but not as a perfect cube or cylinder, but more like a volcano > crater. What happens next is all dependent on the rheology of the paste. > We > found that pastes with little lower viscosity never gave any bubbles, > while > 'thicker' or 'drier' pastes had a tendency to build a 'depression' in the > middle. This was only seen for very small apertures. In our case, we > could > ignore the phenomenon, didn't have any negative impact. We learned this > all > > from our thickfilm printing guy. Wished I had saved all hundreds of > technical report from the 60s and 70s (it was the time we had people who > knew about rheology) but they are gone. Later generations thought this old > stuff was useless, a lot not even stored for the IT age... Trike Man may > still have something hidden in his drawers,,, > > Inge > > > > ----- Original Message ----- > From: "Inge" <[log in to unmask]> > To: <[log in to unmask]> > Sent: Wednesday, July 30, 2008 2:21 PM > Subject: Re: [TN] Solder Paste with craters. > > >> Do you use a thick stencil? >> Have you tried to slow down the stencil lift speed? >> >> Inge >> >> >> ----- Original Message ----- >> From: "Leif Erik Laerum" <[log in to unmask]> >> To: <[log in to unmask]> >> Sent: Wednesday, July 30, 2008 1:56 PM >> 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 >>> >>> >>> >>> 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 >>>> >>>> --------------------------------------------------- >>>> 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 >>>> ----------------------------------------------------- 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[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 -----------------------------------------------------