Thanks Amol.  The CM just told me that he can get a custom fixture made to grip the boards but it costs $850 (I guess thats an "each" cost) so I'll pass to him your suggestion.

 Bob

Sent from my iPhone

On Feb 20, 2012, at 11:40 AM, "Amol Kane (Asteelflash,US)" <[log in to unmask]> wrote:

> Hi Bob,
> While your CM is doing what is very common in the industry (adding SMT
> rails for manufacturability), I would be concerned with the ESD
> implications of sanding, as well as FOD on the assembled product.
> Furthermore, We do not prefer tab routing (mouse bites) due to the
> shock/impact to the board during de-paneling.
> 
> I would recommend you investigate a scored/routed rail that can be
> de-paneled on a pizza cutter. If there are overhanging components on the
> assembly, you may not have a choice. But, careful design of the mouse
> bites, and the tooling thickness can still eliminate the need to sand
> the edges after de-paneling
> 
> Regards,
> Amol
> 
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
> Sent: Saturday, February 18, 2012 2:23 PM
> To: [log in to unmask]
> Subject: [TN] Sanding board edges after reflow
> 
> Our contract assembler just sent us the following message for a short
> prototype run on a modified design:
> 
> -------
> 
> "I asked the board house to add a 1/4" tab routed strip on the long side
> of the board that P1 is on so that we can put solder paste and place all
> of the top side SMT parts.  We need at least 4mm (0.160") for the
> clamping rails on the machines.  C180, C181, D1, R19 and C27 are to
> close to the edge of the board.
> 
> We will remove the strip and sand the tabs."
> 
> ------------
> 
> It's a 6" x 8" 6 layer board (Sn63 soldered) with SMT parts (including a
> 256 ball BGA and a number of tiny QFN parts).  Apparently the EE who
> designed the changes and the PCB layout person were very tight on space
> so extended circuitry into the area reserved for the reflow oven's
> grippers.
> 
> Should I not be concerned that sanding could cause cracks in the solder?
> The EE told me, as did the assembler, there was nothing to worry about.
> 
> This is the first time this problem has occurred since we began making
> products in 1980.
> 
> Should I pull the job (which is a 5 day turn) on Monday and have the
> artwork fixed to provide gripping areas (which used to be there) ?  
> 
> Or is it safe to do what the assembler had told the board fabricator to
> do?
> 
> Bob Landman
> 
> Sent from my iPhone
> 
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