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Min spacing for land patterns from PCB edge

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fsw

#54088

Min spacing for land patterns from PCB edge | 18 March, 2008

Hi! Can anyone tell me what is the min spacing between PCB edge & land pattern to avoid cracking of components due to mechanical stresses caused while depaneling with cookie/pizza cutter.

Thnx!

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#54102

Min spacing for land patterns from PCB edge | 19 March, 2008

Here's what we suggest: * Keep a 5-mm space between a board edge and a ceramic capacitor. * Mount the capacitor parallel relative to the edge. * Design pads about a half of the termination. * Fixture the board when using your pizza cutter.

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fsw

#54121

Min spacing for land patterns from PCB edge | 20 March, 2008

Thnx Dave! I have not seen anyone as yet using fixtures to support brds while using Pizza cutters. Will check it out.

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#54126

Min spacing for land patterns from PCB edge | 20 March, 2008

Min spacing will be 0.75'' on all the 4 edges

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#54127

Min spacing for land patterns from PCB edge | 20 March, 2008

FSW,

Another suggestions is if you have rail on your product and you are concerned about stress fracturing certain components you could add a routed slot to add relief in that area. So when you snap the rail off their would be no stress in that area due to you routed a slot in that part of the rail.

We do this for a couple of our clients.

other wise Standard spacing most board houses would like to see is.

If Routed : .015 If Scored : .020

Regards,

BoardHouse

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#54133

Min spacing for land patterns from PCB edge | 20 March, 2008

Boardhouse: Not to be confruntational, just trying to better understand what you're telling us. When you say, "Standard spacing most board houses would like to see is" blablabla. * What are the units of these dimensions? * You'd like to see these dimensions for what reason? * Are these dimensions selected to facilitate your or your customer process?

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#54134

Min spacing for land patterns from PCB edge | 21 March, 2008

Boardhouse, would it be possible to attach a picture of such a routed slot together with a V cut? I was always told the 2 don't work together that well because of tolerances.

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#54148

Min spacing for land patterns from PCB edge | 24 March, 2008

Is this what you are looking for? We do this on quite a few boards and it has eliminated component problems from the Cab depaneler (pizza cutter)

Attachments:

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#54157

Min spacing for land patterns from PCB edge | 25 March, 2008

Thanks Steve, that's very clear!

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#54165

Min spacing for land patterns from PCB edge | 25 March, 2008

Hi,

I did a large DOE on this a couple of years ago. The smaller the component the closer to the edge you can place. 0201s crack less than 0805s. Also capacitor dielectric comes into play COG,NP0 > X7R >Z5U,Y5V. Y5Vs crack more than NPOs. Ceramic resonators crack often as well. I found that the chop style like the Fancord VPD5 is the lease stressful of the V-Score cutters. We have run as close as 0.025" to the edges with 0805s with no cracking on 0.062" thick PCBs with VPD5. We do this because we have to and not because we want to do it.

Chris

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#54186

Min spacing for land patterns from PCB edge | 26 March, 2008

If you have jobs where you can not, there is a company in Japan that makes the best v-groove depanelers called TST, 'guru's in v-groove depanelising'. Their systems can be supplied to reduce stress on cutting to near zero compared to CAB and other lower cost, lower tech systems. Machines on offer have dual top blades that enables your to pre-cut then cut again thus lowering the separation. They can measure the stress being induced on your assemblies during cutting process and tune the blade profiles and setup of your machine to suit your target PCB's. Of course the v-groove profile-quaility is very important and impacts on stress also.

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#54246

Min spacing for land patterns from PCB edge | 1 April, 2008

Dave,

Sorry for the slow response, have been out of town,

The spacing I was referring to was from board edge to copper features. This spacing is required to keep the router and score blades from exposing or hitting the Copper.

Regarding the slot I was talking about: Steve uploaded a perfect example of what I was describing, Thanks Steve.

Regards,

Boardhouse

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#54321

Min spacing for land patterns from PCB edge | 9 April, 2008

We use a FKN pizza cutter and found that even with 5mm clearance and the proper orientation of the part larger ceramic capacitors 1812, 1210 would still stress fracture. We have successfully fixed stress fracture problems by adding routed relief slots to take the stress of depannaling away from the area of the ceramic capacitor.

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