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February 2012

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 20 Feb 2012 15:14:06 -0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (150 lines)
Depends how much investment your CM is prepared to make - we use a $ 270K 
machine which is fully CNC controlled which can either rout out the boards 
OR saw the boards out of a panel depending on the requirement and also has 
program controlled auto tooling set up..

Best regards

John Burke
General Manager
Zollner Electronics Inc.

From:   Bob Landman <[log in to unmask]>
To:     <[log in to unmask]>
Date:   02/20/2012 03:00 PM
Subject:        Re: [TN] Sanding board edges after reflow
Sent by:        TechNet <[log in to unmask]>



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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