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Subject:
From:
Russ Steiner <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 12 Feb 1999 08:30:32 -0500
Content-Type:
text/plain
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text/plain (154 lines)
Steve - Yep. It's approx the same.  That's what I've done & seen done many
times, in arrays.  The only difference in the finished goods is that overall
thichness is reduced, but only by the Cu thickness of the missing layers in
the 2L areas, as compared to the 4L areas.  Somewhat related --  are very
high Lcount bd's where the inner layers are "non-existant" in edge card
areas.  On a 12-layer board, for example - the missing copper could be on
the order of ( 10 inners x .0007 for  1/2 oz. Cu) .0035, up to ( 10 inner
layers x .0028 for 2 oz. Cu) .028 missing thickness in that area.  It adds
up to significant numbers on high L count bds.  Kind of puts a
hitch-in-the-get-along when you apply the old +/- .006 thickness tolerance
parameter.  In general, other than having more glass in a "built" up 2-layer
as opposed to a standard stock FR-4 base material of the same thickness, it
has very similar properties and functions the same in any situation I've
done this with.  Even large 4L boards that have voids on inner planes or
isolated inner planes function in these void areas the same as any standard
'non-built-up' 2L bd in those areas, for all practical purposes.  That's
what I had eluded to in my prev response to "TN] Assy: Strange new PCB
Technology?" in regards to the 9bd-3D-bent-every-which-way-assembly from
hadees.  Some of the 9-bds in the array were 2L and some 4L.  I've done the
2L/4L on one panel thing several times, succesfully.  After all - once the
FR-4 4L built-up sandwich comes out of the laminating press, the '2L' areas
are roughly the same thickness, with the same base materials (in slightly
different proportions), same copper weight, etc as a conventional 2L.

Regards, Russ

Russ Steiner, CID
National Sales Manager   Controls/inc.
1 Technology Way     Logansport, IN 46947
Voice 248 887-2970     Fax 248 889-9532
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-----Original Message-----
From: Steve Collins <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Thursday, February 11, 1999 10:59 AM
Subject: Re: [TN] Assy: Strange new PCB Technology?


>Steve;
>
>Don't know if this would work but here goes with a thought. Why not process
>the whole board a 4 layer board and those areas that are required to be 2
>layer just etch off all the copper and have bare laminate. Wouldn't this be
>similar to having a two layer board especially if the board is FR-4? Any
>comments from board vendors or EE out there listening in today.
>
>Steve Collins
>PCB Design Supervisor
>
>----------
>> From: Stephen R. Gregory <[log in to unmask]>
>> To: [log in to unmask]
>> Subject: [TN] Assy: Strange new PCB Technology?
>> Date: Wednesday, February 10, 1999 10:56 AM
>>
>> Hi everybody!
>>
>>      We've got a series of boards that we build for a customer who's
>product
>> is a WEB/CATV sort of system. The main board is what they call their
>home-box,
>> or set-top board. It's got a little of everything on it...a digital
>section
>> around the CPU, some RF circuitry with the metal sheilding, and analog
>areas.
>> The system is working and they've got customers, so the next logical step
>in
>> the product life cycle is cost cutting, figuring out how to do the same
>thing
>> only cheaper.
>>
>>       Yesterday my contact at our customer (the materials manager) asked
>me if
>> I have ever built a board that had two complete and distinct sections,
>one a
>> 4-layer section, and the other a 2-layer section, that was joined by some
>sort
>> of "staple" (that was the best way he could describe it to me) and I
>would
>> process it as one single board. He said he wasn't sure if the "staple"
>was
>> pressed into the PCB somehow, or soldered in. But he said he was sure
>that it
>> was said the assemblers would put it together as if it was one board.
>>
>>       I told him lordy no, I have never heard of such a thing. I've done
>> boards that are different layers connected by a flex circuit or a ribbon
>> cable, and that was a completely separate operation towards the end of
>the
>> process, but never processing two different layer boards at the same time
>as
>> one board...have any of you heard of such a thing? My customer said that
>this
>> was something that a fab house down in southern California had told to
>one of
>> their engineers in their efforts to reduce costs...says that they can
>save on
>> their PCB cost by doing something like that since the only section of the
>> board that needs to be 4-layer is a small area right around the CPU.
>>
>>       My first reaction was holy-taco shell batman, how in the world is
>> something like that gonna stay flat? I can't visualize something like
>> that...is the materials manager just trying to mess with me or does
>something
>> like that really exist?
>>
>> -Steve Gregory-
>>
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