I concur with every word Doug says. What is more, ALL polyethylene bags
can cause contamination transfer from the plasticisers contained within
the polymer (and which may also tend to be somewhat hygroscopic,
depending on the chemistry). Furthermore, commercial polyethylene is
quite porous to gases with MWs up to quite a few hundred, which includes
quite a number of corrosive or other nasty chemicals. It therefore gives
bugger-all protection, to boot (other than psychological). :-(
Just to illustrate this, 3 or 4 decades ago, in another life, I made
bare boards (or rather I directed a factory that did). Our G-10 and,
later, FR-4 laminate sheets of the epoch were individually packed in
ginormous heat-sealed poly bags on the outside of which was stuck an
ordinary self-adhesive paper label giving the specs of the contents.
Inevitably, the copper was visibly oxidised much more under the label
than elsewhere, with every make (for the history books, we used mainly
Formica, Nelco, Perstorp and Micaply!). I mention this to show just how
porous PE film can be.
We went through a study of packing materials for our finished boards. We
ended up using aluminium foil in packs of 10 or 12 PCBs (like household
foil but twice as thick) for the punch and crunch products and this
preserved the solderability, even of bare copper, for 6 months, if
unopened. For more sophisticated (read value-added) multilayers, we used
a trifoil bag, one per PCB. The inside was thin unplasticised
polypropylene, which could be vacuum heat sealed without emanating any
nasties. Then there was an aluminium foil layer and the outside was a
polyethylene layer to give it tear-resistant strength. This packaging is
also used in the food industry (notably for packing rösti and gratin
dauphinois in Switzerland, where we were). Straight polyethylene was the
first one we chucked out, of all the candidates.
Brian
"Marsico, James" wrote:
>
> Hello TechNet...
> Years ago, there was an industry problem with pink polypropylene ESD bags
> causing a degradation of solderability. Does this problem still exist?
> Should we accept components packaged by our distributors in these bags?
> Thanks for your comments,
> Jim Marsico
> EDO Electronic Systems Group
> [log in to unmask] <mailto:[log in to unmask]>
>
> ---------------------------------------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> 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 delivery of Technet send the following message: SET Technet NOMAIL
> Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> ---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
