Custom solder mask

qazwsxedcrfv000 · July 16, 2016, 8:36pm

I am making a design with a small custom QFN part. But when it is exported to a Gerber viewer, the solder masks are too large, leaving no room between the pin pads which will make soldering troublesome. Is there any way/setting/workaround/shortcut to deal with it? Thanks.

Old_Grey · July 16, 2016, 8:45pm

We had this discussion before but couldn’t find anything to change the mask. I had ideas but didn’t try anything.

If you want to do experiments with the above info and find a solution please post it.

qazwsxedcrfv000 · July 16, 2016, 10:24pm

After paying a visit to the source code and doing some experiments, I am convinced that I have resolved my issue by setting the svg “stroke-width” attribute to “-0.5”. But such workaround does come with a display problem in the PCB view in Fritzing.

Old_Grey · July 16, 2016, 10:57pm

Is that changing the stroke-width of the contacts in the copper group?

qazwsxedcrfv000 · July 16, 2016, 11:16pm

Yes, that’s right. Though this attribute does not accept negative values by the SVG standard, it just works.

steelgoose · July 17, 2016, 2:35am

@qazwsxedcrfv000, I take it that you want the solder mask between the pads but don’t want to change the width of the solder pads… is that correct? You want the solder mask to come right to the edge of the pads?

qazwsxedcrfv000 · July 17, 2016, 9:03am

Yes. I want to adjust the solder masks without adjusting the copper layer so that I can follow the design recommendation from the IC maker and make my life easier by reducing solder shorts or bridges on QFN parts… In this case I want to have a margin of ~0.07mm between the copper pad the solder mask window.

steelgoose · July 17, 2016, 12:48pm

The solder mask margin in Fz is about 0.1mm. I take it that the solder mask window is about 0.1mm±. I guess Fz needs to have a way to address this issue… There is a way to do it… it takes a little creativity. If you would like me to show you a work-around, post the .fzpz and a link to the data sheet and I will work on it…

Update:
Fz originally was going to include defining solder-mask in a layer in the pcb.svg… http://fritzing.org/forum/thread/2312/

Fz is supposed to automatically expand the solder-mask border by 6mil, 3mil (0.0762mm) around the pads, http://fritzing.org/forum/thread/1125/. Although, I don’t see that unless it does not show up in the Gerber test. I ran three different Gerber test programs and none of them showed a solder-mask window between the QFN, 0.215mm spaced solder pads. One of the test produced an .svg… the solder-mask border measured out at about 0.125mm.

I created a QFN with 0.5mm pin spacing and 0.15mm solder pads… the spacing between the solder-mask keepout from the Gerber test, solder-mask. svg measured about 0.1mm (0.125mm solder-mask border). A QFN with 0,5mm pin spacing and 0.285mm solder pads showed a total blackout for the solder-mask. Again, I set the solder pad width to 0.13mm and measured a solder-mask window of about 0.12mm. So all test show, if the Gerber test .svg is correct… Fz has a solder mask border of about 0.125mm and not 0.0762mm… Oh-Oh… did I fine a bug…

Quick Fix: Create 2 sets of Gerbers… One normal set and a second set with the QFN solder pads set to a width of about 0.13mm or whatever you prefer… then pull the solder-maskTop.gts from the second Gerber set and place it in the normal set of Gerbers.

qazwsxedcrfv000 · July 18, 2016, 4:35pm

I am not really a C++ programmer per se but I think I can still understand its codes.

In gerbergenerator.cpp line 61,

const double GerberGenerator::MaskClearanceMils = 5;

And in svg2gerber.cpp line 34,

static const double MaskClearance = 0.005; // 5 mils clearance

I suppose these mean the clearance is set to 5 Mils, i.e. 0.127mm which is in line with your test results…

github.com

fritzing/fritzing-app/blob/master/src/svg/gerbergenerator.cpp

/*******************************************************************

Part of the Fritzing project - http://fritzing.org
Copyright (c) 2007-2016 Fritzing

Fritzing is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

Fritzing is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Fritzing.  If not, see <http://www.gnu.org/licenses/>.

********************************************************************

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github.com

fritzing/fritzing-app/blob/master/src/svg/svg2gerber.cpp

/*******************************************************************

Part of the Fritzing project - http://fritzing.org
Copyright (c) 2007-2016 Fritzing

Fritzing is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

Fritzing is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Fritzing.  If not, see <http://www.gnu.org/licenses/>.

********************************************************************

This file has been truncated. show original

steelgoose · July 18, 2016, 4:54pm

I was right in the middle of reading your post when you withdraw it… I didn’t understand a word you said anyway…

I kind of thought the solder-mask border may have been set to 5 mils instead of 3… It appears you found the source of the problem… Have you tried to change it to 3 mils to see what happens?

Apparently they changed it to 5 mils or some reason or another…

qazwsxedcrfv000 · July 18, 2016, 5:10pm

I have discovered some lines that are at odd with my own workaround results… I am unsure how come my workaround works at all now… That’s why I have that post withdrawn. I am sorry for any inconvenience caused.

I think I really need to clone its source code and setup the proper toolchain to give it a closer look…

steelgoose · July 18, 2016, 5:24pm

This is way over my head… I would think that if it is suppose to be 3 mils instead of 5… then this should be corrected on the next release I would think 5 mil would be fine for most parts but not for the QFNs and other little bitty buggers… If they leave it at 5 mils then there should be an override… although, I suppose that would just complicate the code…