CADSTAR SMD pad stack when swapping component to bottom layer

[swen_s]

If I define an SM pad that has a default, solder paste top and solder resist top define. And when I use it as a pad to an SM component CADSTAR doesn't handle the swapping correctly when placing the component on the bottom layer.

I also need to define solder paste bottom and soldel resist bottom to make it work.

Why is it so?

 

[Ow@i$]

Since SMD pad will solder on the layer on which they are being placed, so you have to change the layer of the pad depending upon where you want to place it, right click and set the pad properties to bottom layer

 

[swen_s]

Since SMD pad will solder on the layer on which they are being placed, so you have to change the layer of the pad depending upon where you want to place it, right click and set the pad properties to bottom layer

I don't mean when I define the component. I mean when I place it on the layout.

If I have define a small solder paste mask for the top layer it is defined as big as the default if placed on the bottom layer.

 

[Mattylad]

Swen is talking about reassingment's.

If you reassign a top layer I.E. with solder resist and solder paste in your assignments then you need to also reassign the bottom ones too.

Because reassignments do not swap.

When reassigning any pad code always do it for both sides and you will have no problems.

Why is this? I do not know, perhaps because CADSTAR is extremely flexible and allows the user to have different reassignments top AND bottom.

BTW, IPC standards tell us now to keep our solder resist at 1:1 (let manufacturer oversize them to suit their process), you can do that for the paste too and ask the screen manufacturer to reduce all pads by a percentage.

 

[marce]

I would second also not oversizing these days.
As to re-assigments not swapping, it is a pain and causes endless upset, and I cannot see any reason why they cant do it!
And finaly hows the dried cod Mattylad:grin:, you obviously very busy on your holiday...

 

[swen_s]

Swen is talking about reassingment's.
Why is this? I do not know, perhaps because CADSTAR is extremely flexible and allows the user to have different reassignments top AND bottom.

Thank you.

Could you give an example when a surface mounted device needs different size solder mask on top vs bottom?

 

[marce]

There is none, I have never done different solder masks for top and bottom for an SMD component, ever. Nor can I see any reason why re-assignments should not swap, it causes more problems than it would ever solve, it is a feature I have never needed in my PCB design life and imaging I never will.
The only possible reason may have been for wave soldering SMD components, as some liked to have hugh pads for the wave side (why, I never know, the geomatry of the solder joint is the same for top bottom, reflowed or wave soldered), but again soldering SMD by wave these days is a no no with a lot of components, and the ones you can you use the same pad size top or bottom.

 

[Mattylad]

Swen, there is no reason to have different solder paste on top/bottom and these days its best kept to 1:1 however some do prefer to reduce the paste shape per pad themselves when working with different thickness screens and a mixture of fine and large pads.

Copper feature though, this can sometimes be required, as a typical example I once had 3 legged LED's where the centre lead shorted to an adjoining pad. So I made the top pads small circles yet was able to still have larger and different shaped pads on the bottom.

Not swapping is historical as is the whole pad setup.