We have been producing and storing PCB's for many years using this
methodology and have accounts using board more than 3 years old.
Jeffrey Bush
Director, Quality Assurance and Technical Support
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302-1890
Tel. 802.257.4571.21 Fax. 802.257.0011
[log in to unmask]
http://www.vtcircuits.com
-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Wednesday, March 24, 2004 8:54 AM
To: [log in to unmask]
Subject: Re: [TN] pcb storage
Sorry, cannot agree with you. 1) polyethylene bags provide zero
long-term protection. Small gaseous molecules, including water vapour,
pass through the stuff like a sieve 2) vacuum packing is even worse,
because the pressure inside is much lower than the osmotic pressure of
the water vapour outside. 3) In addition, plasticisers in the PE will
sublime out of the bag and can condense onto the PCB, both during and
after the sealing process. If you must bag the circuits, with or without
vacuum, use tripack bags with PE on the outside, aluminium foil in the
middle and polypropylene on the inside. The PE gives the bag the
robustness it needs; the aluminium makes it hermetically impermeable and
the PP provides a non-plasticised, non-contaminating, heat-sealable
interior. This is why tripack bagging is used for some foodstuffs
designed for long-term storage at room temperature - straight plastic
bagging will not work, nor will it for PCBs.
Rather than vacuum, it is better to use dry nitrogen which provides a
slight overpressure, so that minute pores in the sealing will not draw
in air.
Desiccant bags should not be placed in contact with the PCB. Any
desiccant powder on the PCB (and it can be ground off the silica gel
crystals and implanted into the solder mask if vacuum sealed) may cause
electrical failures in humid service.
Furthermore, I suggest your remarks re OSP may be due to using
inadequate packaging materials. An OSP-finished circuit packed
individually or in bulk in tripack bags with dry nitrogen will preserve
its solderability for at least 2 or 3 years.
Been there, done that!
Brian
Jeffrey Bush wrote:
> PCB finishes will dictate storage conditions. HASL and ENIG finishes
> are generally preserved well beyond a year when stored in Poly bags in
> an environment 65-75 F and 40-60 RH. IT/IS finishes should be stored
> in VAC packaging available with most PCB suppliers - you may want to
> add a RH indicator to let you now if any seal failures from handling.
> OSP is basically a finish that should be avoided, but stored in VAC
> packaging, with a indicator and desiccant should preserve this finish
> for at least 6 months although the history of OSP as a preservative is
> not good - mainly was used in captive shops where time to assembly was
> managed easily, as well as rework which seems to be a prerequisite
> with OSP.
>
>
>
>
>
> Jeffrey Bush
> Director, Quality Assurance and Technical Support
>
> 76 Technology Drive - POB 1890
> Brattleboro, Vermont 05302-1890
> Tel. 802.257.4571.21 Fax. 802.257.0011
> [log in to unmask]
> http://www.vtcircuits.com
>
>
>
> -----Original Message-----
> From: Brian Ellis [mailto:[log in to unmask]]
> Sent: Wednesday, March 24, 2004 2:38 AM
> To: [log in to unmask]
> Subject: Re: [TN] pcb storage
>
>
> Dry, cool conditions, in sealed hermetic containers (preferably
> metal), but NOT in polyethylene bags.
>
> Brian
>
> Rey Degollado wrote:
>
>
>>Hello guys,
>>
>>does anybody has an idea on what suitable storage condition for pc
>>boards (humidity / temp.)? we just want to know how to store solder,
>>gold and osp finished boards.
>>
>>
>>Thanks,
>>
>>
>>Rey Degollado
>>
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