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Author Topic: [SOLVED] SMD solder mask - SMD pads  (Read 743 times)

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Offline anishkgt

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[SOLVED] SMD solder mask - SMD pads
« on: August 04, 2017, 12:46:35 AM »
Hi All,

I am trying to etch a PCB before i send it to the fab house. Since this is first time working with SMD components, i am not sure if this would be  the solder mask for SMDs.

Could anybody please help me find the correct solder mask for SMD. In the attached i've enabled only the tCream. The SMD pads here are on the top right as white.

« Last Edit: August 04, 2017, 08:10:43 PM by anishkgt »
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Online ebastler

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Re: SMD solder mask
« Reply #1 on: August 04, 2017, 05:56:15 AM »
You may be confusing two terms here:

Solder mask is the laquer coating (most often green, but other colors are available) which covers most of the PCB, expect for the pads where you want to solder. Those must remain free of solder mask, so the solder can reach and wet the pads. Eagle shows the areas which are kept free of solder mask in the "tStop" and "bStop" layers. This applies to SMD as well as through-hole components, and the tStop and bStop layers show both, SMD and through-hole pads.

The "tCream" and "bCream" layers in Eagle show where solder paste will be added. This is only relevant for SMDs. These layers will not affect your PCB itself in any way. They will be used to manufacture a stencil (a separate piece of sheet metal or plastic to use as a mask for applying the paste), if you order one from the PCB manufacturer.
« Last Edit: August 04, 2017, 05:59:28 AM by ebastler »
 

Offline anishkgt

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Re: SMD solder mask
« Reply #2 on: August 04, 2017, 05:58:27 AM »
Actually yes. I nearly got confused. What I meant was solder pad like the through hole ones.


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Offline latigid on

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Re: SMD solder mask
« Reply #3 on: August 04, 2017, 03:59:31 PM »
Try layer 29/30 (t/bstop) as suggested. Pads are special as they include a drill, mask on both sides and copper on both sides. You could also create a pad from individual elements, but normally it's easier and doesn't give tonnes of DRC errors.
« Last Edit: August 04, 2017, 04:02:09 PM by latigid on »
 

Offline anishkgt

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Re: SMD solder mask
« Reply #4 on: August 04, 2017, 06:03:02 PM »
I guess it did not make much difference. Should it be one solid color ?
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Online ebastler

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Re: SMD solder mask
« Reply #5 on: August 04, 2017, 07:18:35 PM »
I guess it did not make much difference. Should it be one solid color ?

In my Eagle (version 7.6), both the Cream and the Stop layers are shown as hatched areas, not solid. Cream has slightly heavier lines than Stop, so if you display both Cream and Stop layers, you can tell them apart. The direction of the hatch is mirrored for bottom vs. top layers. I believe I never messed with the display scheme, so that should be the default way of rendering it.

Your screenshot shows the (non SMD) pads as solid white. Do you have the "pads" layer shown as well, by any chance?
 

Offline anishkgt

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Re: SMD solder mask
« Reply #6 on: August 04, 2017, 07:35:25 PM »
Yes I have the pads shown in green. I need those for the etching process. The through hole pads and the SMD pads are chosen when applying the solder mask.


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Online ebastler

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Re: SMD solder mask
« Reply #7 on: August 04, 2017, 07:41:57 PM »
Yes I have the pads shown in green. I need those for the etching process. The through hole pads and the SMD pads are chosen when applying the solder mask.

OK, then everything looks to be alright. Does it all make sense for you, or do you have remaining questions?
 

Offline anishkgt

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Re: SMD solder mask
« Reply #8 on: August 04, 2017, 07:51:08 PM »
My concern is when it is not a sold color for each pad would that affect when etching.

When applying solder mask the through hole solder pads would be covered but here the SMD pads are hatched and being hatched, wouldn't that affect how the solder mask is applied. 


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Online ebastler

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Re: SMD solder mask
« Reply #9 on: August 04, 2017, 08:01:14 PM »
But the hatched areas are only shown in the PCB view inside Eagle, right? They need the different colors, hatching patterns etc. there so you can tell the layers apart when you have enabled multiple layers for display. When you export Gerber files for production, these will show the outlines of the areas, without hatching.

Alternatively, if you just want to print a layer for homebrew etching, select "Filled" in the Options section of the Print dialog. (I hope that option is called "filled" in English; I just realized that my Eagle version speaks German...)
 
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Offline anishkgt

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Re: SMD solder mask
« Reply #10 on: August 04, 2017, 08:10:04 PM »
Thank you that solved it.

The layers i chose were
  • Pads (17)
  • Vias (18)
  • Dimension (20)
  • tCream (31)

While printing check 'Solid' as well
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