Lisa:

I too doubt the integrity of plated through holes if they must be broken in half.  In my experience, with .059 
and .031 lamminates, a router will cut through the barrel and leave the connection electrically intact, but the 
remaining plating is somewhat messy and has poor adhesion to the laminate.  The half hole will contain part of 
the copper from the portion that was removed by the router (vertical burrs?)and part of the remaining half will 
be separated from the laminate.  In extreme cases, the half of the hole that was to be removed by routing 
ended up being pushed into the remaining half.  The remaining half hole does not have good adhesion to the 
laminate.  If the board were processed through a good desmear process, the adhesion would be improved.  I have 
strong reservations about using any other method than routing, such as v-score or punch, that would place more 
stress on the plated hole.

An alternative method could be to rout the board outline in a window frame arrangement with two or more 
attachment points prior to metallization.  Non-standard cleaning steps to remove router dust are required.  
This will lead to a board with plated edges.  (A small land measuring .010 to .025 wide on both sides of the 
board is recommended to anchor the plating to the board.)  The finished board should be separated from the web 
by a punch or cutter rather than by twisting or bending.  In an application where more than one signal must 
transition from side to side, the area that is cut by breaking the retention tabs will isolate the signals.  If 
the design permits, it might be advisable to use redundant vias in parallel with the edge plating.

In designs where edge plating was required on double sided boards for improved shielding or for soldering the 
board into a metal can, testing proved that the plating could be eliminated without degrading the performance 
of the design.

In summary, routing will leave a connection between the two sides, but the reliability (robustness) of the hole 
is questionable.  I have no experience with punching or v-scoring but suspect that the remaining plating, if 
any, will be even less reliable.  I also suspect that the metal deformation on .010 core laminate will be less 
spectacular than the deformation on .059 laminates.

Don Vischulis
[log in to unmask]

PS A hacker got to my provider's mail server and it is acting strange.  Please forgive me if there are multiple 
copies of this message.
-----------------------------------------------------------------------
Lisa Williams wrote:
> 
> ---------- Forwarded message ----------
> Date: Tue, 16 Jul 1996 17:47:11 -0500
> From: Fred Pescitelli <[log in to unmask]>
> To: [log in to unmask]
> Cc: [log in to unmask]
> Subject: Thin laminates
> 
> All,
> Has anyone any experience using .010 FR4 for double sided boards? Also I
> need to place 4- 0.025 dia plated thru holes centered on the edge of the
> board. The board will be have to be panelized, so it will either be
> V-Scored, punched, or routed (right through 1/2 of the dia of the holes. I
> have been told that some companies are doing this, but I am sceptical.  I
> can't believe there will be any plating left. Has anyone done this, or do
> you have any thoughts on the matter?
> 
> Regards
> Fred Pescitelli
> Phoenix Designs
> 1285 Turner Rd.
> Lilburn, GA   30247
> [log in to unmask]
> 770-923-3465
> 
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