Hi Genny,
If you reference J-STD-033B, there is a derating table at the end that allows you to add (or reduce) allowable out of bag time based on your operating environment. Given your dry conditions, you could conceivably change a level 3 device's out of bag time to infinity. The crux is determining the sensitivity level of each board... (Based on experience, I'd say boards are a level 2.5 - 3, but since I'm in a similar boat, I will have to actually do the testing to nail it down for my product.)
Also, the board shop should be the one baking your boards prior to packaging and using a MBB!
You are fortunate to have immersion silver boards, I once did bake testing on immersion silver (48 hours at 125ºC) and saw no change in solder ability. No surprises there. Immersion tin and OSP were unsolderable after the same test.
Concerning the desiccant, the cardboard packaged desiccant is the bad desiccant for silver. There are other decants that are safe for silver. However, I am quite cynical about using desiccants. I've yet to see a packing department store desiccant in a moisture proof container. An open container is not moisture proof. And the desiccant is not a catalyst, so once the desiccant is saturated with moisture, it doesn't work as a desiccant anymore. You might want to at least check your own packing department for proper desiccant storing and handling, and ideally audit the board shop for proper desiccant handling.
Anyway, good luck,
Ryan Grant
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Monday, December 03, 2007 9:02 AM
To: [log in to unmask]
Subject: Re: [TN] Delamination of lead free PCBs
I am dragging up this 5 week old thread due to our fabricator just sent
us the Isola doc and told us we need to bake our boards.
I have two questions regarding this document in relation to Immersion
Silver.
It mentions packing with desiccant, but ImmAg docs always recommend no
desiccant, due to the potential for tarnish. How do you resolve this?
We live on the frigid prairies, so humidity is generally WELL under 20%
at this time of year around here. I am thinking, allow the manufacturer
to use desiccant if they package the boards with silver saver paper, and
then we remove the desiccant as soon as it arrives here, and just
repackage in MBB with a humidity card only?
Second dilemma: The Imm Ag recommendations say to bake boards with this
finish tightly wrapped in tinfoil. Wouldn't that inhibit the moisture
even getting out of the boards during baking?
Thanks for your time
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin D Asbell
Sent: October 24, 2007 11:53 AM
To: [log in to unmask]
Subject: Re: [TN] Delamination of lead free PCBs
The information in that document contains very best practices that the
better board shops have been applying for years...I don't get how this
is being viewed and/or received as "new methods or requirements" for
board shops and assemblers???
I've read the Isola document, it does not contain anything new, it just
looks like someone (industry leader et al) finally wrote down what many
shops have been doing, and all shops should be doing...
I'm curious Ian, are you getting a stipend for pushing Isolas article?
(this was just a joke)
Franklin D Asbell
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ian Hanna
Sent: Wednesday, October 24, 2007 8:13 AM
To: [log in to unmask]
Subject: Re: [TN] Delamination of lead free PCBs
The Isola document referenced by Cheryl Tulkoff a few posts ago --
09-12-07 is a clue
<http://www.isola-group.com/images/file/TechnicalBulletinleadfreeprocedu
res091207.pdf>
I've heard talk of this from other laminate vendors but Isola has been
the first to bring this formally to the fabricators attention.
Ian
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joel Alexander
Sent: Wednesday, October 24, 2007 8:54 AM
To: [log in to unmask]
Subject: Re: [TN] Delamination of lead free PCBs
Can you provide the document names that were published in August
Joel Alexander
Quality Assurance Manager
TT APSCO, INC.
Ian Hanna <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
10/24/2007 08:47 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Ian Hanna
<[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Delamination of lead free PCBs
These specific guidelines for lead-free were first published in august
of this year -- this guidance is a departure from that given for modern
laminates, from roughly 1990 on up...
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: Wednesday, October 24, 2007 6:26 AM
To: [log in to unmask]
Subject: Re: [TN] Delamination of lead free PCBs
(chuckle) A recent requirement!!!
If your board supplier told you baking to remove moisture is a 'recent
requirement' then they are either very unknowledgeable about their
laminates or just plain deceiving you.
In either respect, good luck on being reimbursed.
Franklin D Asbell
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: Wednesday, October 24, 2007 2:46 AM
To: [log in to unmask]
Subject: Re: [TN] Delamination of lead free PCBs
We just had a similar thing happen, with FR4 HR370. Before we did'nt
bake prior to assembly as the boards came direct from the board house,
now we are seeing de-lam. They told us that it is a recent requirement
that came from the material supplier that they forgot to inform us of.
Ours are 12 layer, stacked vias. Currently we trying to get some money
back!
Ian Thomas
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