Dennis,
Thanks. What ratio is the acceptable norm?

Thanks and regards,
~wee mei~

From: Dennis Fritz [mailto:[log in to unmask]]
Sent: Thursday, June 21, 2012 11:10 AM
To: Lum Wee Mei; [log in to unmask]
Subject: Re: [TN] Etch Factor

From IPC T-50:

Etch Factor (term - 54.0452)
The ratio of the depth of etch to the amount of lateral etch,
i.e., the ratio of conductor thickness to the amount of
undercut. (See Figure E-2.)



















-----Original Message-----
From: Lum Wee Mei <[log in to unmask]<mailto:[log in to unmask]>>
To: TechNet E-Mail Forum <[log in to unmask]<mailto:[log in to unmask]>>; Dennis Fritz <[log in to unmask]<mailto:[log in to unmask]>>
Sent: Wed, Jun 20, 2012 8:09 pm
Subject: RE: [TN] Etch Factor

I happen to be looking for the same query as Shawn - what is the acceptable or

comfortable etch factor number? I remember someone telling me many many years

ago that this etch factor is 1 but I have forgotten whether it should be greater

than or less than.



Thanks and regards,

~wee mei~



-----Original Message-----

From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Dennis Fritz

Sent: Thursday, June 21, 2012 4:00 AM

To: [log in to unmask]<mailto:[log in to unmask]>

Subject: Re: [TN] Etch Factor



Shawn,



Etch factor is determined by many factors - etching chemistry, metallic plating

or photoresist defining the copper to be removed, spray pressure in the etcher,

top or bottom of the board travelling horizontally through the etch machine, pH

of the etching solution, ability of the shop to time the board travel (slower

means over etch, faster means underetch), etc.



Etching is something of a chemical art, rather than a precise mechanical

operation like drilling.



I suggest you work with your fabrication shop process engineers.  They know what

etch factors they can produce, and the straighter you want your copper conductor

walls, the more care (hence higher price) your fabricated board will become.

Most any etch factor is possible - artwork line width compensation, tuning the

etcher for your specific boards, running the boards fast twice and flipping the

boards top to bottom between runs, etc.  However, each of these steps costs time

and productivity, and you will pay for it.



There is one sister industry to PWB board fabrication that makes a living only

etching metal sheets - photochemical machining.  They etch from both sides

making relatively staight sidewall parts, in 1 to 50 mil metal thickness, in

various metal alloys, and compete with die stamped flat parts. They have the

ultimate knowledge of etch factors.



Denny Fritz







-----Original Message-----

From: Upton, Shawn <[log in to unmask]<mailto:[log in to unmask]>>

To: TechNet <[log in to unmask]<mailto:[log in to unmask]>>

Sent: Wed, Jun 20, 2012 11:52 am

Subject: [TN] Etch Factor





Ok, got my specifications, looking at IPC-2221A Figure 10-3, for conductor width

see section 10.1.1 also, pages 77&79); and IPC-A-600H 3.2.1 (see page 86).  It

ooks like "etch factor" drives how much of a trapezoid one has on any given

race, although outer layers (since they are plated) may have overhang.

What I don't see is any qualitative numbers: ie, an etch factor of y +/-z is

ypical for outer layers, vs w for inner layers.  Are these numbers variable rom

vendor to vendor; and have to be called out on any given FAB drawing, since here

isn't a generic number to be pointed at?

Shawn Upton, KB1CKT

est Engineer

llegro MicroSystems, Inc

[log in to unmask]<mailto:[log in to unmask]>

03.626.2429/fax: 603.641.5336



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