Mel,
What's your interpretation of the 5 thermal cycles - do they include the
thermal cycling used to fabricate the PCB in the first place? And what
temperatures are we talking about? Does, say, a bake cycle at 90 degrees
count, or are we talking reflow temperatures? Just curious.
Peter
Mel Parrish <[log in to unmask]> 19/12/2002 11:16 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Mel Parrish
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] PCB Repair Criteria
Much of the ability to survive rework or thermal excursions is dependent
upon the fabrication materials. The board qualification criteria under the
55110 was designed around 5 thermal cycles, which if you add them up, gives
you one rework process if it requires extraction and site preparation.
After
that all bets are off. The qualification other than 55110 is less robust
so
you can see what you might be up against.
Good Luck, Mel
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Victor Hernandez
Sent: Thursday, December 19, 2002 8:34 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Repair Criteria
The repair site is a Power FET on a .062 PCB with 4 layers. This is the
Vcore plane. Perhaps 1oz.
victor,
-----Original Message-----
From: Charles Caswell [mailto:[log in to unmask]]
Sent: Thursday, December 19, 2002 8:30 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Repair Criteria
This is a difficult question to answer. The simple answer is none.There are
too many factors involved. Lead to hole ratio, copper weight, skill of
operator and equipment used are all variables to consider. I have removed
and replaced a 172 pin PGA 15 times in a 15 layer board with no apparent
damage. Although I'm sure there was some degradation to the life expectancy
of the board. This board was later used as part of the flight
qualification,
-40 to +85 degC severe vibe etc. and passed. I will be watching for other
replies to this one.
Charles Caswell
-----Original Message-----
From: Victor Hernandez [mailto:[log in to unmask]]
Sent: Thursday, December 19, 2002 7:55 AM
To: [log in to unmask]
Subject: [TN] PCB Repair Criteria
> Fellow TechNetters,
>
> Can some one assist me with this question. How man times can a
PTH
> component be
safely removed before damage to the inner connections on the barrel occurs.
> Victor G. Hernandez
>
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