Take me off distribution.  You have the wrong Michael Patterson

-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Denny
Cantwell
Sent: Monday, September 13, 2004 12:53 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Etchback Question

Tino et el,

There was a study conducted by Dwayne Poteet of Texas Instruments (and
his crew) regarding the reliability of "etchback (positive)", smear
removal only, and "negative etchback"---back in 1982 when the
committee's were working on MIL-P-55110, MIL-P-50884, MIL-STD-275 and
MIL-STD-2118.  The studies may not be available after all of this time,
but from memory,  all of the conditions listed passed the <10% max
increase in resistance when subjected to Thermal Shock per IPC-TM-650
Method 2.6.7.2 for 100 cycles.  The "negative etchback" of
.0005"(0.013mm) allowance was also established at that time.  The
thought process was that if the copper interface was clean enough to
etch negatively from the "as-drilled" condition, it was also clean
enough to electroplate reliably.  These values were in all of the above
referenced specs and continued in MIL-PRF-55110F (PAGE 11) PARA A.3.6.5,
A.3.6.5.1, A.3.6.5.1.1, and A.3.6.5.2 plus the others that I don't have
on hand.

If, as you state, that the end customer is a military org., then the
parts produced had to have had coupons on the panels.  If you propose to
the customer, or the military end user, that the "D-portion" of the
coupon be subjected to Thermal Shock per above for 100 minimum cycles,
or 400 cycles, or even to destruction, then you should be able to
establish a "reliability-factor" that will satisfy everyone.  The
"functionality" of the device would thus be established independently of
a "visual" determination of where and how much etchback is present in
the "A/B" coupons used for microsectioning.
Regards,

Dennis J. Cantwell
Q.A. Mgr./R & D Liaison
Printed Circuits, Inc.
1200 West 96th Street
Minneapolis, MN 55431-2699
952-888-7900
[log in to unmask]


-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
Constantino J. Gonzalez
Sent: Monday, September 13, 2004 11:59 AM
To: [log in to unmask]
Subject: [IPC-600-6012] Etchback Question

Hello help....

My question is, do you have any knowledge of any studies having been
performed regarding reliability of ethchback vs. non, or low etchback on
innerconnect joints of polyimide PWBs?

My customer is asupplier for an aerospace company, and the issue is that
they recently have found through microsection analysis that some boards
they have already installed in a vehicle are suspect, with regards to
etchback.  I am looking for supporting documentation to disposition the
boards.  Our requirement is for etchback per 6012 CL III, but I don't
believe they are necessarily un-usable. The sections are otherwise
structurally sound, no post or plating sep, 1oz and greater conductors,
etc.

As always, I appreciate any info you might be able to pass on.

Regards,

Tino Gonzalez