Thank you everyone for helping out with this.
I'm sorry to not send an individual thanks to all, but I've read all the
responses and appreciate them all.
This sipad approach has generated a lot of interest, so I hope it works out.
The cover layer I believe is purely a mechanical device, so that the top
surface is completely smooth once the electronics are epoxied over.
My best wishes to you,
Richard

----- Original Message -----
From: "Dehoyos, Ramon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 23, 2005 11:52 AM
Subject: Re: [TN] solder paste deposit on internal layer?


>
>
>         It is called SIPAD. Try www.sipad.net 770.475.4576 or colonial
circuits 800.578.9602
>         Ramon
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Hal Winslow
> Sent: Thursday, June 23, 2005 10:49 AM
> To: [log in to unmask]
> Subject: Re: [TN] solder paste deposit on internal layer?
>
>
> 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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