Chris,
Only when I was working with Microsoft building mice. Those were CEM1 boards as well. We tried punching FR4, but it cracked in places - boards in mice are small and the features are close. (The material is more brittle than CEM or FR2.) If you keep all copper features 30 mils from the edge, and all drilled holes and cutouts 60 mils from the edge, you might be able to avoid any damage. (Those #'s are from a fuzzy memory...better double check me.) Be sure to get the limitations from the fab shop for your features. Ask them to show you samples of FR4 multi-layer boards they've punched. Get close up pictures of the possible failure points. Ask them to show you failures.
Since you've been using CEM1, you know that it punches easily because it's a softer material. My guess is that they've been using an FR2 for your 2 sided boards. Which is a step up from CEM1, but less heat tolerant than FR4. FR4 is more brittle and harder. It will wear down the edge of the punch tool much faster and those punch tools aren't cheap. If the fab shop still thinks this is faster and more efficient (it may be that the fall-out may offset time on the router), and you can meet the spacing requirements, I'd try it.
My 2 cents,
Cherie Litson, CID+, CII
Sr. PCB Designer
Sonosite, Inc.
425-951-1306 wk
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of
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Sent: Tuesday, September 21, 2004 1:31 PM
To: [log in to unmask]
Subject: [DC] punching 4 layer board
Hi All-
I need to know if anyone is getting multi-layer boards with punched
features today. If so, some feedback on the quality. One of our assembly
houses wants to move some high volume boards to a new supplier who has
already tooled up to punch the arrays.
We've used millions and millions of punched CEM1 PCB's and a few million
punched FR4 2 sided. Never had any problems attributed to the punch vs.
routing process.
Need to know if if 4 or 6 layer FR4 is another story or no different than 2
sided FR4.
I'm not talking about plated through features, just the board outline (many
boards in an array).
I asked this before and got a little feedback; at the time there was no
feedback from anyone doing it. It seems some of these low cost chinese
houses do nothing else. Has anyone else run into this?
Thanks in advance,
-Chris
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