Working with Solder Stencil openings

[iitgrad]

In the latest version of KiCad, which layer is the one to use for creating a stencil. After reading other posts I’m thinking there is a default size reduction that is global across the entire PCB that can be set but I wasn’t able to find it in pcb editor. I’m making some stencil here in the lab with our laser cutter and normally I wouldn’t worry about this, but I have 1 QFN accelerometer part that is very small so I want to get the stencil perfect if possible.

[Rene_Poschl]

@iitgrad

which layer is the one to use for creating a stencil.

F.Paste and B.Paste. See What is the meaning of the layers in pcb_new and in the footprint editor?

@iitgrad

After reading other posts I’m thinking there is a default size reduction that is global across the entire PCB that can be set but I wasn’t able to find it in pcb editor.

File->board settings (somewhere in there)

@iitgrad

but I have 1 QFN accelerometer part that is very small so I want to get the stencil perfect if possible.

Make sure the center pad is made correctly (reduce paste coverage and paste areas split up. All footprints that ship with kicad have a reduction to 65% which is in the middle of the range i found suggested by manufacturers). Otherwise, you run into problems at the reflow stage (bad connections of outer pads as there is too much solder in the middle, problems with trapped gases, …).

[iitgrad]

Thanks @Rene_Poschl. I had to make this pattern myself as I was unable to find a pre built pad layout. There is no center pad.

The pad dimensions were set based on the “PCB Land Pattern” which I’m hoping is the right one to use.

[Rene_Poschl]

You also have very little clearance at the corners so i might suggest using chamfered pads. You can generate footprints with our scripts found here: https://github.com/pointhi/kicad-footprint-generator/tree/master/scripts/Packages/Package_NoLead__DFN_QFN_LGA_SON

Chamfering of edge pins is used by https://github.com/pointhi/kicad-footprint-generator/blob/d88a9cf913c4c2f6bacb96413fce7cfa3180514a/scripts/Packages/Package_NoLead__DFN_QFN_LGA_SON/size_definitions/qfn/qfn-28.yaml#L304

[eelik]

@Rene_Poschl

suggest using chamfered pads

Chamfered is a wrong word here - chamfered will be possible in 6.0. Rounded works in v5.

[Rene_Poschl]

One can make chamfered pads with custom pads. This is why i pointed to the generator that implements an abstraction for that. (We will most likely continue to use the workaround even in v6 as chamfered pads do not support rounding corners. See https://gitlab.com/kicad/code/kicad/issues/2383)