Scott is right, punching boards is probably the most cost effective way to
produce large quantities of panels... but there are design requirements for
punching that need to be taken into consideration before going down that
path. First I would want to know the end use of the design and determine if
the punching process might degrade the board performance to the point that
it would not be useable in the application it is intended for.

I'm curious if in this case other materials more suitable to punching were
investigated like CEM1 for instance...there are alternative materials
manufactured that are far less abrasive to the punch and die tooling than
FR4.

If I was doing a board for high volume punching I would be very concerned
about the QC procedures and inspecting lot samples. The choice of materials
would be critical in determining the life of the tool which is a somewhat
considerable investment. The life of the tool would definitely be
foreshortened due to the abrasive nature of the FR4 materials if that was
the only material I could use. Glass/epoxy laminate tends to suffer from
fracturing of the glass when punched, especially in the inner layers opening
the potential for moisture intrusion and entrapment and delamination of the
glass and epoxy bond which is undesirable too... you need to know if your
product must survive in a humid environment...  Use of FR4 would make
frequent tool sharpening a requirement and I would think the clearance from
the board edge and cutout features would need to be increased to protect the
inner layers from frayed edges and broken fibers. Possibly conformal coating
would be needed after assembly to prevent moisture from getting into the
board or some other protective process would be needed to compensate for the
lower quality edges.

I have not researched it yet but I would suggest you go look and see if IPC
has any specifications on edge quality acceptability and include it in the
notes on the face of the drawing before making a high volume production run
with punched FR4. At least this one note would give you the legal grounds to
reject any non-compliant material that was shipped from your vendor because
they were forewarned of your acceptance criteria.

P.S. I did not get a photo with your e-mail but if you post it with Steve we
can all take a look at it.

His website is http://www.stevezeva.homestead.com/


Best regards,

Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com


-----Original Message-----
From: Scott B. Westheimer [mailto:[log in to unmask]]
Sent: Thursday, February 17, 2005 8:26 AM
To: [log in to unmask]
Subject: Re: [TN] Cracking FR4

FR4 has been punched for years. I first worked in Asia in 1985 and worked in
Asia for over 14 years. Almost all of work is punched except for
multi-layers because of the fracturing between layer concern. If the
supplier has good controls they count the number of hits and resharpen the
tools. Layer count, board thickness and dimensional tolerance should dictate
to them if they can use a punch press or not.

Scott Westheimer
----- Original Message -----
From: "Greaves, Bernie (IMP)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 16, 2005 10:54 PM
Subject: [TN] Cracking FR4


Hopefully someone in the forum may have had experience with cracking
along edge of FR4 as per attached photo. The profile of this pcb was
punched and subsequently the edge has fine cracks through the soldermask
and glass. We have had a large quantity of this part made in China and
are concerned that this cracking could compromise the board function.

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