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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