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July 2008

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Subject:
From:
Leif Erik Laerum <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Leif Erik Laerum <[log in to unmask]>
Date:
Thu, 31 Jul 2008 08:54:49 -0500
Content-Type:
text/plain
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text/plain (228 lines)
The fines appear mostly on resistor pack and capacitor packs and they 
are more prevalent on the bottom side (First reflow). We are going to 
reduce these apertures a bit.

Leif Erik Laerum
Quality Assurance Manager
Texas Memory Systems
[log in to unmask]
Tel: (713) 266-3200 x468
www.texmemsys.com



Tan Geok Ang wrote:
> Actually this is not uncommon; the point is that whether is it too
> large? Concentrate on fine pitch components, and determine whether the
> post reflow solder joints result is acceptable or not. I believed that
> you will not face any issue due to this "problem".
> But if you use, Solder paste inspection machine (inspection on stencil
> or on the deposited paste on PCB) you will have to "wait" await to
> minimise rejects.
>
> What is the flux % which you asked for? 
>  
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven
> Sent: Thursday, 31 July 2008 5:46 PM
> To: [log in to unmask]
> Subject: Re: [TN] Solder Paste with craters.
>
> Leif,
>
> You have received so many great suggestions thus far that I feel
> somewhat silly asking this, but ...
>
>    You are using a metal squeegee, correct ... !?
>
> I will go back to my corner now...
>
> Steve
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
> Sent: Wednesday, July 30, 2008 12:31 PM
> To: [log in to unmask]
> Subject: Re: [TN] Solder Paste with craters.
>
> I have not see that kind of print anomaly. Obviously this will change
> the
> solder volume and it is undesirable. While the craters are not causing
> the
> fines. They could be symptomatic of a failure in the material that
> results
> in fines. 
>
> The flux should dry and then the solder coalesce onto the feature at
> reflow.
> Some pastes fail in so that the flux runs all over carrying the solder
> spheres with it off the pads. Then at reflow the flux burns off leaving
> fines stranded everywhere.
>
> I have run into this problem and I have receive bad solder paste from
> reputable suppliers that do this fresh from a sealed jar. 
>
> You could observe this with a BGA rework station, hot air or IR pen.
> Compare
> the problem paste with fresh paste and paste that does not produce
> fines.
> I think you will see a difference. 
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
> Sent: Wednesday, July 30, 2008 11:59 AM
> To: [log in to unmask]
> Subject: Re: [TN] Solder Paste with craters.
>
> Hi Leif!
>
> I have your pictures posted. Go to:
>
> http://stevezeva.homestead.com/files/air_bubbles_and_craters_1.jpg
>
> http://stevezeva.homestead.com/files/air_bubbles_and_craters_2.jpg
>
> Is the percentage of metals the same as your leaded paste? I also think
> the
> rheology the paste won't be the same with as it is with the leaded
> paste, so
> there will most likely have to be changes with the set-up of the print.
> It
> almost looks like the separation speed is too fast, and the paste isn't
> given time to pull away from the inside of the apertures causing the
> crater...
>
> Steve
>
> -----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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