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Forum Index : PCB Manufacturing : A result that I cannot understand

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OA47

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Joined: 11/04/2012
Location: Australia
Posts: 911
Posted: 07:36am 03 May 2024
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I have been successfully creating CNC routed prototype PCB's for some time. Over the last week I have been experimenting with laying a solder mask over the routed PCB and the milling off the mask on the solder pads. I have not been at all successful and I cannot fathom the cause of the results. I am using K-CAD to generate the G-CODE for the job and using the electric sensing probe to set the tool height. I hope my problem is demonstrated with the attached picture.



 

The red board has been isolation routed and as you may be able to see some of the pads have been completely cleared away and others are perfect. I used a 60 degree 3.125mm chamfer bit and my first thoughts were that the variations in the thickness of the PCB would cause this issue.

The second attempt (labelled 3) is the lower black attempt that isolation routed ok, this time I used a 2mm conical bit and it shows generally the same pads being cut through although this is a newer area of the blank PCB. The G-code definitely shows the Z depth to be consistent over the job when I checked the code.

The third attempt (black, labelled 2) was using a 0.1mm flat conical bit (no isolation routing prior) and again the pads previously destroyed are the same ones even when others are missed completely.

I am at a loss to see what is happening here and how I can fix it.

0A47
 
phil99

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Joined: 11/02/2018
Location: Australia
Posts: 1813
Posted: 07:48am 03 May 2024
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Unless you are planning on wave soldering these boards, it may be easier to wait until after the components have been soldered to apply the coating.
That is how I have been doing it for half a century.
 
greybeard
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Joined: 04/01/2010
Location: Australia
Posts: 158
Posted: 07:57am 03 May 2024
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Is the sensing probe optical? if so it might be 'confused' by the coating and/or a reflection.
Edited 2024-05-03 17:57 by greybeard
 
OA47

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Posted: 07:58am 03 May 2024
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Phil the reason that I want to have the solder mask is to prevent solder bridges when attaching the components.

0A47
 
OA47

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Joined: 11/04/2012
Location: Australia
Posts: 911
Posted: 07:59am 03 May 2024
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Greybeard, the probe sensing is electrical contact between the PCB and the tool.

0A47
 
phil99

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Posted: 08:04am 03 May 2024
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  Quote  solder mask is to prevent solder bridges
Fair enough. Doesn't help me though. I have a talent for bridging pins regardless and always have to finish with solder-wick on SMDs.
 
OA47

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Joined: 11/04/2012
Location: Australia
Posts: 911
Posted: 08:07am 03 May 2024
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  Quote  I am using K-CAD to generate the G-CODE for the job


Sorry for the memory slip. This should have read.

I am using Flat-CAM to generate the G-CODE for the job

0A47
 
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