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August 2011

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Subject:
From:
Tan Geok Ang <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Tan Geok Ang <[log in to unmask]>
Date:
Thu, 4 Aug 2011 11:27:20 +0800
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Agreed but maybe I should rephrase my question.
To meet a thickness of 3.5mils, what I know is that the fabrication
process will need at least 2 prepreg to meet this requirement. Believed
not under the following prepreg material 106, 1080, 2113, 2116, 7628.


-----Original Message-----
From: Frank Kimmey [mailto:[log in to unmask]] 
Sent: Monday, 1 August 2011 10:11 PM
To: 'TechNet E-Mail Forum'; Tan Geok Ang
Subject: RE: PCB dielectric - 2 layers prepreg

I think mostly for fill.
As an example, 1080 prepreg starts at about 3.5 mils and after pressing
is about 2.5 mils.
This means there is about 0.5 mils per side to fill in etched areas on
adjacent layers.
That is less than 1/2 oz copper (currently IPC considers 1.2 mil
thickness  per oz).
Poor fill will aid in delamination and poor reliability.
Use of 2 sheets will allow more resin to flow towards needed fill areas
giving better bonding.
Also resin content on thinner prepregs is usually higher allowing more
resin flow to use for fill

A Designers understanding of why

Frank N Kimmey CID+
Manager - PCB Design
Powerwave Technologies Inc
Mobile - 916-670-0645

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang
Sent: Sunday, July 31, 2011 6:50 PM
To: [log in to unmask]
Subject: [TN] PCB dielectric - 2 layers prepreg

Hi All,
		In one of the Class 3/A Exception Requirements, it
indicates that for "Dielectric Thickness of 0.089 mm [0.0035 in] minimum
with 2 layers prepreg if not specified on drawing.", what is the reason
to use 2 layers prepreg, what is the advantage over a single layer?
Thanks.

Regards
GA Tan
 		
		

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