Thanks Graham, Phil & Ted.
The CM says ESD isn't a problem because his employee wears a wrist strap and the sander is grounded...
I gave up - no point trying to explain how friction generates charges.
He refused to take Amol's advice, said the pizza cutters he looked at were NG.
Looks like its time to find a new CM.
Bob
Sent from my iPhone
On Feb 20, 2012, at 1:46 PM, Bob Landman <[log in to unmask]> wrote:
> 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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