One very important reason for using a higher melt solder is stand-off
height..ceramic BGAs are considerably heavier than plastic ...if eutectic was
used, the chances for bridges increases, the higher the ball pitch would have to
be and the lower stand-ff would make it more difficult to clean if necessary...
marcelo
-----Original Message-----
From: Ed Holton [SMTP:[log in to unmask]]
Sent: Tuesday, September 15, 1998 10:10 AM
To: [log in to unmask]
Subject: Re: [TN] X-ray for open joints on BGA's ?
I am curious, why are the ceramic BGA solder balls not eutectic and made
with the 90/10 Pb/Sn solder?
[log in to unmask] on 09/14/98 11:30:26 AM
Please respond to [log in to unmask]; Please respond to
[log in to unmask]
To: [log in to unmask]
cc: (bcc: Ed Holton/Hella North America Inc.)
Subject: Re: [TN] X-ray for open joints on BGA's ?
Hi Daan,
Two comments come to mind:
1) Remember that not all BGA solder balls are eutectic (and therefore
collapse during reflow). CBGA devices typically use 90/10 Pb/Sn solder
which don't melt during reflow. Opens are much more common with these.
2) I've had some experiences with some large PBGA devices having opens
around the periphery during rework, but generally with packages which
showed a marked tendency to "potato chip". This was much more
noticeable
when solder paste wasn't used (some folks just use a tacky flux).
Personally, I never found much use for X-ray on BGA devices in a
production
mode. Develop the process (which may or may not entail the use of
X-ray)
and control the critical parameters, and you'll find the instances of
BGA
solder joint defects is extremely low.
Best regards,
Greg Bartlett
Teledyne Electronic Technologies
Hudson, NH
[log in to unmask]
-------------------------
Hello Technet,
I remember a discussion a couple of weeks ago about X-ray inspection.
It
was stated that the nr.1 defect that one wishes to see with a X-ray
machine
is open joints, but unluckily this type of defect can only be seen with
the most expensive X-ray machines on the market.
I was thinking : if the BGA (the balls) collapses during soldering and
is
soldered perfectly parallel to the board surface, all the balls must
have
reflowed ! If only one of the balls didn't melt, the component can not
be
soldered parallel to the board surface !
Since the chance that a collapsed ball forms a joint with the pad is
almost 100 % , it can be concluded that X-ray inspection for "opens"
does
not make much sense. Just looking at the parallellity should tell you
enough !!
What do you think, is this a reasonable thought or am I overlooking some
things ??
Regards,
Daan Terstegge
Signaal Communications
* Unclassified *
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