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Reply To: | TechNet E-Mail Forum. |
Date: | Fri, 16 Nov 2001 16:33:02 -0500 |
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Hello Peter,
Symmetrical stack-up is crucial and I've seen a few designs where it just
couldn't be helped (impedance). Rapid or uncontrolled cool down during
lamination can also contribute to bow/twist in a balanced construction.
I've successfully used post lamination dewarp procedures similar to Jeff's
suggestion but that was for Class 2 stuff. The trick is making the dewarp
last through subsequent high temp. assembly steps (soldering).
Hans
Integrity First - Service Before Self - Excellence in All We Do
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Hans M. Hinners
Electronics Engineer
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
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Robins AFB GA 31098-1622
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-----Original Message-----
From: <Peter George Duncan> [mailto:[log in to unmask]]
Sent: Thursday, November 15, 2001 9:11 PM
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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