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November 2001

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Subject:
From:
"Zhu, Xiang" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 16 Nov 2001 10:32:05 +0800
Content-Type:
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text/plain (65 lines)
Please check you design first. If this design have an uneven copper pattern
/ stack-up/ soldermask thickness, the warpage is very hard to avoid. My
suggestion is use a fixture to force the board come back to flat in
assembly. But, please take care about the potential tension strength after
fixture removal, for tension will cause BGA solder joint crack.
Good Luck!
Ben

-----Original Message-----
From: <Peter George Duncan> [mailto:[log in to unmask]]
Sent: Friday, November 16, 2001 10:11
To: [log in to unmask]
Subject: [TN] Board Warp


Hi, All,

We have received a number of 12 layer ENIG-finished MLB's with blind via
hole groups, and which are destined to have BGA's (1.27mm pitch) populated
onto them. The boards measure 8.2" x 5.7" and they are warped to the extent
of one corner being raised by between 1.5mm and about 3mm. The axis of the
warp is the long side of a triangle whose other two sides measure about 5.7
x 5.7.

In this age of sensitive boards, does a technology or technique exist for
straightening the boards back into spec - they are class 3 boards - or is
this an area where angels still fear to tread?

The boards are desperately urgent, which is why I'm asking this rather than
simply rejecting them and having them re-made (which takes about a month).

TIA for any help.

Peter Duncan

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