Ashok,

I typically see 1-2 mil over-etch, but that is on 1/2 oz copper and I am
guessing that no adjustments have been made from the gerber data prior
to fabrication. I would assume that 1 oz or 2 oz copper would have even
more etch, and that you (your board vendor) would need to start
adjusting for the etch.

Ben

-----Original Message-----
From: Ashok Dhawan [mailto:[log in to unmask]] 
Sent: Monday, May 19, 2008 9:23 AM
To: TechNet E-Mail Forum; Gumpert, Ben; [log in to unmask]
Subject: RE: [TN] Solder Pad width
Importance: High


Ben

It is not that simple as you do not start with 20 mils pad. There is
provision for etching which varies. 
I was looking for actual pad width measured on production boards at 20
mil pitch TSOP or QFPs if someone is using 2 Ozs copper. Interestingly,
cross-section of Pad is not rectangular in shape. It is more like
trapezoid. Topside is narrow and base is wide. For printing, topside of
the pad is relevant surface for gasketing with stencil apertures. 

I will appreciate your experience in measured data (topside of pad)

regards


Ashok Dhawan
Manufacturing Engineer
Parker Hanniffin Inc
Winnipeg Canada

-----Original Message-----
From: TechNet on behalf of Gumpert, Ben
Sent: Mon 5/19/2008 8:00 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Pad width
 
Ashok,

Looks like you answered your own question.
20 mil pad design - (2.5 mil etch x 2 sides) = 15 mil pad actual > 10
mils 

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ashok Dhawan
Sent: Thursday, May 15, 2008 9:05 PM
To: [log in to unmask]
Subject: [TN] Solder Pad width

I am looking for measured pad width for 20 mil land pattern for SMT.
(QFP or TSOP) 

What is Pad width actal versus top copper layer?  Copper outer layer is
1 oz or 2 oz or 3 ozs. 

Reason for this question: Stencil is 6mils thick with min aperture
opening of 9 mils. For gasketing, the pad need to o=be over 10 mils. 

2 Ozs copper has etch factor 2.5 mils over etch each side. Can final pad
width of over 10 mils be made.

Any inputs on this will be appreciated.

Regards


Ashok

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