First you eliminate the materials and then address the process
temperature profile. Profile the heat distribution on the entire board
surface for consistency. The temperature is not high enough to
adequately melt the solder sphere and solder paste and/or lack of flux.
Collecting the variable will lead you to the outlier and thus corrective
action. What recent changed has taken place in the assembly line.
Conduct a fish bone diagram.
Who owns responsibility for RoHS compliance in your product
There is no straight forward solution and/or short cuts
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 10:36 AM
To: [log in to unmask]
Subject: Re: [TN] Separation in BGA joints
Victor,
I like your itemized answers. Please see below.
Q: Is this the only BGA on you board?
A: < No, and it's the smallest one.
I also have a transformer, slightly bigger in footprint, but
pretty
massive. Everything solders like a charm.>
Q: Is this artifact found on other products?
A: <Yes, on 2 products, both have the same issue>
Q: Are the PWB finishes the same on all products?
A: <All ENIG>
Q: Has this BGA been REWORKED/RESTENCILED/REBALLED?
A: <Nope, straight from the original tray.
Unless something has been done by the part manufacturer.
I'll check on that>
Q: Is this an outer ROW solder bump or INNER?
Q: <Random and several balls per part>
Comments: It is not a good practice to use LF sphere with SnPb solder
paste.
Reply: < As I said, we tell this to our customers, but they cannot
find leaded part. Since they do not have LF for other parts, they take
responsibility and ask us to run leaded process. And it's more and more
of them. But I am talking consumer goods>
Now, can you please elaborate on the pillow thing, what is it? A well
known defect?
Thanks,
Ioan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 9:58 AM
To: [log in to unmask]
Subject: Re: [TN] Separation in BGA joints
George, Victor,
foot-in-the-mud, head-on-pillow. It seems that you two are talking about
the same thing, but what is it and why is this happening?
The stencil is 6 mils thick with square apertures, the dimension equal
to the diameter of the pad. ENIG finish.
Time above liquidous is 65s.
Due to pressures from our customers we run many lead-free BGAs on leaded
paste at 220C. If this forms joints, why LF on LF would not form joints
at 246C, or let's say 230C if I am really off in my temp measurements?
Thanks,
Ioan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Tempea, Ioan
Sent: Wednesday, November 15, 2006 9:57 AM
To: [log in to unmask]
Subject: [TN] Separation in BGA joints
Hi TNLF-ers,
please have a look at http://stevezeva.homestead.com/files/Ioan_Ball.jpg
, many thanks to Steve again.
What can I tell you: no-clean SAC305 at the bottom, the balls read a
sort of SAC with 3%Ag and 1.75%Cu The reflow profile seems to be OK, I
measure 246C under the periphery of the BGA, with a thermocouple that is
squeezed there. I know it is not rigorous, I did not drill, I am not
measuring inside the joint. But even if I am 20C off, the materials
should be molten and coalesce, isn't it?
The intermetallics solder paste - PCB pad are OK, the wetting is good,
the BGA balls seem to have changed shape, they are almost collapsed,
there is physical contact between the balls and the paste, but no joint.
The question is: why do I see the separation line? What can cause that?
Should I bother investigating the process, or do I have a sort of
contamination? Or the BGA ball alloy has a higher melting point?
Thanks,
Ioan
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