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I am new to making PCB's and I have a question. I have an IC and I need to make pads for it on my board. ON many PCB's I observed that the area where I place the pin has some metallic material on it so the pin sticks to it correctly. What layer is this. The place where I solder the resistor and capacitor(the leads is often metallic and silvery). IS this the cream layer. Or is it something else?

enter image description here

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  • \$\begingroup\$ While all the info below is correct, you shouldn't have to worry about any of this in any reasonable layout program-- aside from whether you want the chip to be on the top or bottom of your circuit board. If you can't simply insert a through hole pad and have all the layers-- creams, masks, etc, come out correctly, you're using the wrong package, or approaching it in the wrong way. Certainly, if you need to carefully tweak some mask for reasons that may come up as your boards get more complex, you'll need to know this stuff, but it doesn't sound like you're there yet. \$\endgroup\$ – Scott Seidman Dec 6 '13 at 13:35
  • \$\begingroup\$ But you have to define the pads somewhere? (I'm familiar with Allegro and its external padstack editor) \$\endgroup\$ – pjc50 Dec 6 '13 at 15:20
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A pad should exist on several layers:

  • on the copper layer, on the correct side of the board
  • then a cutout in the soldermask (coating over the copper, usually transparent green)
  • (optionally) on the solderpaste layer. This might be the cream layer you're referring to. You need this if you will be mass producing it with a solderpaste stencil. Pads that are defined on this layer recieve solder paste during assembly, then the parts are added and the whole thing is baked in an oven to solder all the parts at once. Often this is only for surface mount parts.
  • (optionally) the part should have an outline and reference designator (R1 etc) on the silkscreen layer. This is the white printed text. It's not functionally required but helps in assembly.

Edit in response to image:

That looks like "tinning" (thin layer of tin or solder over the copper). Tinning is one available PCB finish; gold plating ("ENIG") is also popular. It's the default on OSHpark, for example.

To achieve what's shown in your image, put the pad on "copper" and "soldermask", then request tinning from your PCB manufacturer. The traces will only be on the copper layer and will not be tinned.

Note that pads on the copper layer define where there is copper, and on soldermask specify where the holes in the soldermask are.

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  • \$\begingroup\$ Edited the question . PLease take a look \$\endgroup\$ – Developer Android Dec 6 '13 at 11:10
  • \$\begingroup\$ See edit: copper+soldermask+tinning. \$\endgroup\$ – pjc50 Dec 6 '13 at 11:19
  • \$\begingroup\$ FWIW: "ENIG" = Electroless Nickel, Immersion Gold. It's a coating process. \$\endgroup\$ – Connor Wolf Dec 6 '13 at 11:20
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    \$\begingroup\$ @DeveloperAndroid, typically tinning affects all exposed copper, so it doesn't require a layer in the design files. It is possible to mask some areas so they don't receive tinning, but this is uncommon. You would do it by making an extra non-standard layer and giving the fab shop special instructions to mask the areas indicated on that layer from tinning. \$\endgroup\$ – The Photon Dec 6 '13 at 17:33
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    \$\begingroup\$ That's what the soldermask does: it covers the traces but not the pads, so tinning doesn't apply to the traces. \$\endgroup\$ – pjc50 Dec 7 '13 at 14:40

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