Hi Jens,
I noticed that no one answered your question, so I'll try to throw in my 2
cents.
As far as I know, it is not very common to use top layer for routing. One
may use it in order to protect the outer layer features from the pressure
foot of the router. Many people use a brush type pressure foot that doesn't
damage the outer surface usually but in case you have very delicate
features - you might want to protect them even so.
Another case when you would need this protection, even while using a brush
type pressure foot is when you rout an already assembled board (yes, I've
seen people do it).

Another case is when someone decides to use a hard insert for routing (I saw
it only on a few occasions). Then you would better protect the outer surface
of the board.

The use of an entry board for routing is also common to prevent the
formation of burrs in cases where the raw material is rather soft (like
PTFE) or the PCB has full copper planes extending until the edges.


I don't think that this type of application can be used in order to prevent
small PCBs from flying around, since the entry board (your protective FR-4
sheet) is routed out at the same time with the PCBs. It means that you might
even have some more pieces flying around. One of the methods to prevent this
is to rout them out with break-away tabs.

I hope it helped a little and feel free to contact me for further
discussion.

Best regards,
Yehuda Weisz


----- Original Message -----
From: PCBA <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, March 15, 2001 7:58 AM
Subject: [TN] routing top layer material - yes or no?


> Hi all,
>
> we have been approached to supply top layer material for routing.
Basically
> unclad FR4, 0.80-1.00mm.
>
> As this application is a bit new to me, does everybody uses a top layer
> when routing PCBs?
> If not, under what conditions will you use top layer material?
> And what types are most common?
>
> I presume they want to route small PCBs and they don't want the PCBs to
fly
> around once they cut lose.
>
> Your feedback will be appreciated.
>
> regards
>
> Jens
>
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