TECHNET Archives

November 2001

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Hinners Hans M Civ WRALC/LUGE <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 16 Nov 2001 16:33:02 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (70 lines)
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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Electronics Engineer
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
Special Operations Forces System Program Office (SOF - SPO)
Gunship Team
226 Cochran Street
Robins AFB GA 31098-1622

mailto:[log in to unmask]

Com: (478) 926 - 5224
Fax:   (478) 926 - 4911
DSN Prefix: 468


-----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

[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]

---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------

ATOM RSS1 RSS2