Requirement on warpage here is maximum 100 microns for all BGAs. And the warpage we seem to have in a case is some 200 microns. Measured by taking the three balls that the package rests on and then measure diff from that level. Max 100 microns is tough for a package BGA that is 50x50mms. Any opinion about that?
Jim, your point about down rating is good, I agree 100%. In fact solidifying is just something we don't know much about. Even if we had an LA copper here shouting 'FREEZEŽ you can't be sure all balls change from liquid to solid simultaneously. I just can't believe that. And while in this cycle, the BGA tries to relax. There seems to be an interesting field for thinkers here.
We are going to study the drop-off with a new IRvideorecorder (not using conveyour oven of course) we have and hope to see something out of the isotherms. At least a try. If it works, I will send a line or two. Anyone who ever tried this?
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: Jim Kittel [mailto:[log in to unmask]]
Sent: den 28 februari 2001 14:33
To: [log in to unmask]
Subject: Re: [TN] Heat-sinked BGA Bridging...
Steve,
I have been working this issue with some very large 'glob top' BGA's and had
to modify the first cool down zone to get the BGA's to flatten out. Some
oven manufacturers (like mine) seem to have a race to get the boards back to
room temp after solder (a marketing ploy) and blast the board with
relatively cold room air right out of the spike zone. You don't see much
effect with the thermocouples buried under the BGA, but try placing one on
top and watch the temperature dive. This top/bottom temperature
differential is what caused my warpage. My fancy 8 heating zone/2 cooling
zone oven had no provisions for adjusting the cooling zone so I used wire
cutters to disable the two top blowers. What a difference! Works for me.
Jim Kittel
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Tuesday, February 27, 2001 2:34 PM
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-
----------------------------------------------------------------------------
-----
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
----------------------------------------------------------------------------
-----
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
