I worked with a flex circuit that had heat sinks on the back side of the
SMT components. The SMT Process was handled using carrying pallets. To
keep costs , and the number of pallets, down we developed two cooling
racks at the end of the reflow oven. It was a metal rack on a cart with
8 fans on it. The pallets would stand vertical in the rack using guide
rails with ~.5" between each pallet. It didn't take long for them to
cool off enough to be wheeled back to the screen printer and be loaded
back up with no interruption to production. This was used on a high
volume product and because there was a left and a right sided assembly
the pallets were double sided and saw a lot of use. They held up very
well except for, the area that hit the bump stop. We had to add a metal
insert because the pallet wore out in that area before the pallet needed
to be replaced. 

Regards,

Ted T.  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Monday, February 20, 2012 12:52 PM
To: [log in to unmask]
Subject: Re: [TN] Sanding board edges after reflow

In cases like this (the joys of contract manufacturing) we have had
carrying pallets made, for more like $250 each.  We had one board that
was donut shaped, can't do much with that!

Using a carrying pallet will increase the handling time, but is likely
cheaper than re-spinning the PWB.

regards,
 - Graham
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Monday, February 20, 2012 2:47 PM
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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