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With a successful through-hole design under my belt I am now ready to try fabricating a board that uses surface-mount components. I have been reading about this, and have gathered that the DIY crowd has gotten reasonable results with "hot plate" reflow soldering.

I think I understand the basics of this technique, but one point on which I am still unclear is the necessity of a solder resist coating. Is reflow possible without it?

I have seen a kit from LPKF for adding a solder resist coating to a prototype board, but do I really need it?

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  • \$\begingroup\$ do you have a stencil? \$\endgroup\$ – vicatcu Jan 19 '12 at 19:01
  • \$\begingroup\$ I am planning to cut a stencil for applying solder paste, yes. \$\endgroup\$ – Kaelin Colclasure Jan 19 '12 at 19:03
  • \$\begingroup\$ I would say that it would probably work better with solder resist. As long as you are using large pitch parts, it should work though. ( I don't know for sure ) \$\endgroup\$ – Brad Gilbert Jan 19 '12 at 19:40
  • \$\begingroup\$ Why don't you try the coating on some to master other aspects, then try some without \$\endgroup\$ – Ali Jan 19 '12 at 20:11
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In general, reflow soldering would work w/o solder resist. You might get a higher incidence of solder bridges without solder resist (solder mask) than with it.

Among other things, the incidence of solder bridges depends on the pitch (spacing) between the pins of the ICs you’re using. Fine pitch pins are easier to bridge. For example, you’d get more solder bridges on SSOP packages with 0.025” pitch than on SOIC packages with 0.050” spacing. What IC packages do you have on your board?

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  • \$\begingroup\$ If I'm reading the spec page correctly, the 40VQFN package has pins pitched at 0.5mm (!) or 0.0197" spacing. \$\endgroup\$ – Kaelin Colclasure Jan 20 '12 at 0:17
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    \$\begingroup\$ If your quantities aren't high you can inspect boards and remove possible solder bridges with soldering iron and solder wick/braid. \$\endgroup\$ – Nick Alexeev Jan 20 '12 at 0:49
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In addition to Nick's great answer, I just want to add that the number of bridges that you get on the fine pitched ICs will also depend on how much solder paste you apply. Obviously the more paste, the more solder bridges you will have.

In my past experience, I have found that adding extra flux to the area will help prevent solder bridges on your ICs.

Also, you will find that solder will take to the exposed tracks, meaning that less will stay on the pad where you want it. This is more of a problem for larger width tracks. I've never had any major issues with this - it is easy to add more solder.

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