Altium -negative solder mask expansion for bga footprint

[waqsoh]

Hi,

I am trying to make bga footrping for first time on altium. My copper pad diameter is 0.406 mm. and Solder mask defined opening is 0.320 mm.
When i try to use solder mask expansion for the pad ,it expands outwards instead of making the copper pad opening smaller. Is there any way to expand solder mask inwards.
Thanks

[qdrives]

waqsoh Options:
1) You need to change the layer transparency.
View / Panels / View configuration
Increase the transparency of Pads.
Top screenshot.

2) Or use single layer mode and look at the solder mask layer

3) Change the layer drawing order.
Tools / Preferences -> PCB editor -> Display
Make sure the the current layer is above signal layers.
Look at the solder mask layer to see that it is smaller then the (copper) pad.

[robertferanec]

try -0.320

[qdrives]

Solder mask expansion should be (0.32 - 0.406) / 2 = -0.043mm (note the negative).
Using robertferanec value of -0.32mm you would completely cover the pad. Robert was just mentioning the negative number 😉

[robertferanec]

qdrives thanks for correcting

[waqsoh]

qdrives robertferanec

I have been already trying the negative number in solder mask expansion but it is not working. Figure 1 below shows that when the copper pad size is 0.407 mm and solder mask expansion rule is 0.1 mm. The measured pad and solder mask dimesnions are correct.

Figure 1. showing corrrect solder mask expansion

However Figure 2 shows that when i choose manual solder mask expansion as -0.043 mm. The solder mask disappears.

This seems like a basic question but i am struggling with it. Thanks for your quidance.

[qdrives]

waqsoh Options:
1) You need to change the layer transparency.
View / Panels / View configuration
Increase the transparency of Pads.
Top screenshot.

2) Or use single layer mode and look at the solder mask layer

3) Change the layer drawing order.
Tools / Preferences -> PCB editor -> Display
Make sure the the current layer is above signal layers.
Look at the solder mask layer to see that it is smaller then the (copper) pad.

[waqsoh]

qdrives Dear, shifting to single layer mode, worked perfectly. Thanks.