Yes ma'am,
agree about tricky ENIG and repair. I examined a computer, pulled out the BGA processor and sliced it into pieces and found a wonderful design without that tricky nickel, balls soldered directly on tinned copper. Old fashioned just-copper seems to be useful still. And that BGA was not a cute thing....rather a monsterBGA! What processor? You certainly guess yourself. Use to be on inside of the box.
Ingemar
-----Original Message-----
From: Bogdan Gabi [mailto:[log in to unmask]]
Sent: den 28 februari 2001 09:53
To: [log in to unmask]
Subject: Re: [TN] Heat-sinked BGA Bridging...
Same component, same problems, but during reflow at the SRT station we own, only corner bridging.Same% of good results.
Rework is done without solder paste, only Tack flux.
We suspect also warping due to Aluminium heat sink, very heavy, glued on the base circuit of the BGA and on chip with conductive glue.
During oven reflow we had solder joint problems at first, changed the speed, got better results, but we are still fighting with this component.
May I ask what is the finish of your board and if you have SMD pads or not?
Related problem:
We work with ENIG and SMD pads, I don't know if it is the best combination, also , as Ingemar told, we are also suspecting bad finish workmanship.
The other BGA's DO NOT exhibit any problems, but only during the first reflow.
If we have to rework them and desolder the bad part, some pads look dull gray and don't cover with solder during circuit pads rework and cleaning.
Thank you,
Gaby
----------
From: Stephen R. Gregory[SMTP:[log in to unmask]]
Reply To: TechNet E-Mail Forum.;[log in to unmask]
Sent: ???? ????? 27 ?????? 2001? 23:33
To: [log in to unmask]
Subject: [TN] Heat-sinked BGA Bridging...
Hi all!
This topic is a "moldy-oldie", but I've started to experience bridges again
with this TI DSP (TMS320C6201GJC200). I've been doing okay up unil recently.
We build these boards in work orders of around 25 pieces.
Our last run we had 7 boards bridged out of 25!! Sent the boards out to be
reworked. I asked that they be x-rayed before and after, and to my surprise
after looking at the x-ray images, they were all bridging in the same general
area.
It's a 4-row periphery BGA, and the bridges are occuring on the inner two
rows, around the center of the part, at the same side of the part.
What's funny, is that the vendor we use to rework the boards for us is having
difficulty as well. We've been asking him to remove, re-ball, and re-install
the part, they said they've been having about a 50% success rate doing
this...they've been getting the bridges too. They have a nice full-blown SRT
BGA rework station and do this for a living.
I print 6-mils of paste (square apertures for the BGA), have a Conceptronic
HVN-70 which I run:
150 160 170 180 240
150 160 170 180 240
25-in. per min
We never have had these problems before...it all started when TI put the
heatsink into the top of the part. I've looked at our paste print and it's
dead on, placement is dead on too, we verify that with a Ersascope.
My question is could there be something wrong with the part? Warping causes
bridges at the corners, right? Why would it bridge in the interior rows at
the same general area?
Thanks in advance!
-Steve Gregory-
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