This might be one of those instances where that Solid Solder deposit
process would work for you. I imagine you would fab the board, do the
solder deposit, apply the cover layer.
You might then have to apply flux before assembly, but supposedly you
can get all the solder you need through that process. I read a certain
amount about it 5 or 8 years ago, but have never used the process
myself.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne Oosterhof
Sent: Thursday, June 23, 2005 10:46 AM
To: [log in to unmask]
Subject: Re: [TN] solder paste deposit on internal layer?
You could look at the cover layer as part of the stencil and use an
additional very thin regular stencil with apertures larger than those of
the
cover layer. The combination of the apertures in the steel stencil and
those
in the cover layer (how thick is it?) could give you the necessary
volume of
solder paste.
It will take some work with a spreadsheet to get all the numbers you
need,
but I believe it could be done. Unless of course you have multiple board
pads in one cover layer opening.
For those locations you could use a needle paste dispenser, which is a
slower method to apply the paste. If the cover layer openings are as
large
as any of the components then a stencil may not work at all. I expect
this
is the case as you have to assure that the components touch the solder
paste, then back to the needle.
The more I think about it the more worms there are in this can.
Ahne.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard
Sent: Thursday, June 23, 2005 0:25
To: [log in to unmask]
Subject: [TN] solder paste deposit on internal layer?
Dear TN Members,
First off, I need to thank everyone for their answers to my question
regarding the construction of an unusually thick PCB. I really meant to
send that out about a month ago but was bad and let myself get buried in
the
next thing...
I am back on that project now, and have received the prototypes which
were
built just fine. In review, this PCB has an external un-etched "cover"
layer made from a sheet of polyimide that is adhered to the top surface
of
the actual circuit carrying PCB.
Now the problem is how to apply solder paste to the pads on the IC lands
that are accessible through cut-outs, below the surface of the cover
layer.
Does anyone know if it is possible for solderpaste to be applied before
a
top layer is fixed? The cover layer is being bonded with a super high
performance 3M adhesive. I don't think it will ever actually be
laminated
in the stack-up, but I could be wrong.
Thank you very very much if you have ever heard of such a thing, or have
any
advice.
I am just a contractor, and the client would require the sigining of an
NDA,
so I am not completely free to pass their information on to the forum.
If
you represent a company I could of course forward your proposals to
management.
Richard
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