I'm sure there is some intermetallic activity occurring between the solder
and copper but I've not seen any recent studies on this with HASL coated
boards. What may bring a bad taste to everyone's mouth is the old tin-lead
reflow process (tin-lead plate then fusing) which did have a bad effect on
the copper from my experience.
This is a good argument for retained coupons and samples for any product
remaining in stock for a period of time. If the need arises for whatever
reason for product to be shipped from 'long term storage' (as opposed to
stock, grin) evaluate the condition of the coating using the retained
coupons or even a representative board.
Have the lab cross section it to determine any copper degradation, do a
thermal stress, microsection looking for separation, voids (after thermal
stress, etc) and other conditions that may be of concern.
We've done this before, usually running two coupons, once without bake, the
other with bake and see no difference from the samples in storage for years
and the original coupons collected and evaluated at time of fabrication.
We attempted before the tin strip and recoat process and found it to make a
worse solderable surface than just leaving it as it is.
I'm not saying this should be standard practice, but if it should meet a
certain need and data shows they function then why not? But I caution to
communicate this to any customer first, get their approval.
Franklin
-----Original Message-----
From: Dehoyos, Ramon [mailto:[log in to unmask]]
Sent: Tuesday, August 09, 2005 3:13 PM
To: TechNet E-Mail Forum; Franklin Asbell
Subject: RE: [TN] PCB Storage
I have encounter resistance from a mentality type of folks
that strongly argue that HASL boards need to be etched and replated
after 12 months. These people recommend TIN/LEAD uplating instead of
HASL if the boards are not going to be used within a year. Their
argument is that the intermetalics in the barrels would render the
boards unsolderable. Any thoughts on this mater?
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin Asbell
Sent: Tuesday, August 09, 2005 4:01 PM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
While I certainly do not recommend this practice, I had some boards in
my desk for 5 years, under some papers, beneath a box...I had
'forgotten' they were there, just for kicks I soldered them without bake
and they looked good.
For storage in an office (or controlled)environment I would suggest
vacuum seal with dessicant for the environment you suggest. Time in
itself for that period should not be an issue, just keep them sealed and
they may last up to
7 years or more.
Franklin
-----Original Message-----
From: Black, Paul [mailto:[log in to unmask]]
Sent: Tuesday, August 09, 2005 2:32 PM
To: [log in to unmask]
Subject: [TN] PCB Storage
Hi All,
I have some bare PC boards that may be built up in the future, but not
in the near future. I would like to put them into storage until needed
(anywhere from 6 months to 2 years). The boards are .062" FR-4 HASL
boards.
What would you recommend for protection, assuming that the storage
conditions are typical of an office environment? Would I have to do
anything special to them when they are removed from storage? Any
suggestions would be greatly appreciated.
Thank you,
Paul Black
Manufacturing Engineer
Kronos
E-mail: [log in to unmask]
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