Nice work Gaby!
Looks very cleanly done.
It's possible Manufacturer 1 just didn't get enough time at flow for the
bubbles to work their way out. I know that when I get SIPAD (pre-flowed
deposits) put on a board that this rarely happens.
Very matte finishes on PCBs always need to be looked at carefully. They
almost always give us trouble. I agree that the likely culprit is
crevices in the surface which suck up vehicle/flux components and take a
long time to let them go. We used to solder to thick film over ceramic
regularly, and that stuff is very "chunky" -- lots of surface features.
Reflowing in vacuum led to dramatic improvements, as did carefully
burnishing all of the pads.
So matte can be good if it is only in the very thin immersion topcoat
because it shows low stress in the plating, leading to less chance for
sending out some kind of whiskers, but matte in the underlying copper
causes problems with void entrapment.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, February 04, 2008 4:54 PM
To: [log in to unmask]
Subject: Re: [TN] Microvoids immersion silver
Hi Gaby!
Just got it up on my site now. I've been buried with my head in our VCD
all day pulling all the tooling out out to do an annual PM. But go to:
http://stevezeva.homestead.com/files/ImAG_from_2_vendors.doc
Steve
________________________________
From: Gabriela Bogdan [mailto:[log in to unmask]]
Sent: Monday, February 04, 2008 1:55 PM
To: [log in to unmask]; [log in to unmask]; [log in to unmask];
Gabriela Bogdan; Lee parker
Cc: Steve Gregory; stephen gregory
Subject: Re: [TN] Microvoids immersion silver
Finished my "investigation". Attached word doc, Steve, could you put it
on your site?
Can anybody comment or give an advice?
Thanks,
Gaby
----- Original Message -----
From: Gabriela Bogdan <mailto:[log in to unmask]>
To: [log in to unmask] ; [log in to unmask]
Sent: Tuesday, January 29, 2008 8:49 PM
Subject: Re: [TN] Microvoids immersion silver
Decided to investigate further to qualify our vendors.
4BGA + 2 circuits and assembly.
Will cross section bare, after paste+reflow, after BGA assembly
and also X-ray and dye and pry.
At least I will have fun.
Gaby
----- Original Message -----
From: [log in to unmask]
To: [log in to unmask] ; [log in to unmask]
Sent: Tuesday, January 29, 2008 8:35 PM
Subject: Re: [TN] Microvoids immersion silver
Hi Gaby,
I take it what you are seeing are 'champagne voids.'
Voids like these are 'encouraged by rough topography
copper, excessive Ag thickness, some solder paste choices and rapid
cool-down after reflow. But as Donald Cullen says in his comprehensive
paper, it "requires the "Perfect Storm" of a rather contrived
combination of parameters" to produce planar micro-voiding.
Well Gaby, now you know it-you are "Perfect." ;-)
Werner
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