If this is class 2 application, both mouse bites and scoring tabs are
proven methods, although not preferred.  I have seen very good machines
use pin routers to depanel commercial PWAs and the controls included
excellent collection methods for the "dust".  Having said that, passives
that are located within the clamping keepout zone are normally a red DFM
flag.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Monday, February 20, 2012 10:47 AM
To: [log in to unmask]
Subject: Re: [TN] Sanding board edges after reflow

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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