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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Thu, 31 Jul 2008 16:15:36 -0700
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text/plain
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text/plain (409 lines)
Ahhhhhhhhhh but he was working for Fry's when I first met him in
1983.......................

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: Inge [mailto:[log in to unmask]] 
Sent: Thursday, July 31, 2008 2:27 PM
To: TechNet E-Mail Forum; John Burke
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
>>>>
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