Follow up:

A novel approach has been proposed which I thought some of you might be
interested in.
This was not my idea but I have to admit that there is more than one way to
skin a cat, as they say.

The shields are being mechanically removed (no heat) from the boards by
cutting and then pulling the remaining pieces out of the solder joints.
The components which can be reworked using a solder iron are then processed.
Components which require hot air still are being reworked in that manner.
A new shield is being soldered using hot air and new tacky flux.
The boards are being marked each time the assembly sees a hot air cycle to
monitor the "health" of its reliability.
Supposedly the shield pads are strong enough to withstand this brute force
approach as the ground metal is flooded on the surface.

Thanks for everyone's comments.

At 12:42 PM 8/9/2004, Phil Bavaro wrote:
>We are discussing the maximum number of rework cycles that an assembly can
>withstand before being considered a reliability risk.
>Historically we have always used five rework cycles as our guideline which
>permitted the part to be taken off, and put on twice during rework.
>
>1.  Reflow oven exposure
>2.  Removal cycle
>3.  Resolder cycle
>4.  Removal cycle
>5.  Resolder cycle.
>
>The first question is where does this requirement actually come from and
>the answer usually is give based on the standard coupon float testing.
>
>But in today world, with one piece shields incorporated, such a simple
>approach is usually not the case.
>
>1.  Reflow first side oven exposure
>2.  Reflow second side oven exposure
>3.  Remove shield cycle
>4.  Remove part cycle
>5.  Resolder part cycle
>6.  Resolder shield cycle
>7.  Remove shield cycle
>8.  Remove part cycle
>9.  Resolder part cycle
>10.Resolder shield cycle
>
>Comments anyone?
>
>---------------------------------------------------
>Technet Mail List provided as a service by IPC using LISTSERV 1.8e
>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 or (re-start) delivery of Technet send e-mail to
>[log in to unmask]: SET Technet NOMAIL or (MAIL)
>To receive ONE mailing per day of all the posts: send e-mail to
>[log in to unmask]: SET Technet Digest
>Search the archives of previous posts at: http://listserv.ipc.org/archives
>Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>for additional information, or contact Keach Sasamori at [log in to unmask] or
>847-509-9700 ext.5315
>-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------