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Is there any difference between a gold coated pad and a gold pad? I have been ordering boards from OSH park, they are really good quality, I'm just wondering what benefits this has over silver or bare copper pads.

What are the benefits of usign a gold coated pad? I do know it must have better conductivity and proably better or lower resistance but, does coating really achieve all this? doesn't the material below the coating affect the conductive properties of the tracks?

enter image description here

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    \$\begingroup\$ Just a quick problem, why use so many 741s while things like LM324 costs less and saves board space? Also since you are using SMD parts you can tuck bypass caps, if small enough like 0603s, under socketed DIP chips without double sided loading. \$\endgroup\$ – Maxthon Chan Dec 22 '14 at 22:39
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    \$\begingroup\$ its a small school project and i had way to many 741s so i decided to use them in this project, did my schemmatic and layout around them since i had no 324s around and i really didnt want to buy more stuff \$\endgroup\$ – GoatZero Dec 22 '14 at 22:41
  • \$\begingroup\$ now that smd tip its really good i will make sure i do it in my next design \$\endgroup\$ – GoatZero Dec 22 '14 at 22:42
  • \$\begingroup\$ I believe LM324 cost no more than two 741s each. And one nice thing about LM324 is that the bypass cap can be tucked right between its power pins, which happens to be right opposite each other on the chip. \$\endgroup\$ – Maxthon Chan Dec 22 '14 at 22:46
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The main purpose of the coating on the pads is to prevent corrosion.

Copper oxidises very easily in a normal atmosphere - it goes green. By adding a coating on the top you are sealing the copper away from the atmosphere and protecting it.

You have a choice of coating, and coating methods, and each has its own benefits.

There are basically 3 methods:

  1. Hot-Air Solder Levelling (HASL)
  2. Electroplating
  3. Chemical plating

The most common "silver" one you see is HASL. This basically involves covering the pads with a thin layer of solder and using hot air to reflow it and level it off.

Chemical plating - dipping the board in a tin solution - is the most common "home brew" method since it is easy to do and the chemicals are easily available.

Electroplating is usually used with gold. Similar to silver and gold plated jewellery. It's very very expensive.

The gold chemical plating (ENIG) is the most common way of depositing gold. It is not as expensive as electroplating, but it does still give very good results. Not only does it give a good clean low resistance contact, but the perfect flat surface is also good for pick and place machines - especially with fine pitched leaded surface mount components (such as TQFP) where the slightly raised pads of the HASL can cause misalignments to happen.

HASL is cheap though, and still gives "good enough" connections.

Also the gold pads just look so much cooler.

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    \$\begingroup\$ The standard gold coating used on most boards is ENIG, electroless nickel immersion gold. It's a chemical process not an electroplating process :) \$\endgroup\$ – Some Hardware Guy Dec 22 '14 at 21:14
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That looks like ENIG to me, thin gold over nickel and it's main purpose is to protect the copper below from oxidation. It actually gets absorbed up into the solder, or solder ball during soldering and allows the solder to make a direct connection to the copper underneath. Too much gold can actually lead to brittle solder joints.

So gold enig vs silver immersion, gold enig is going to have a longer shelf life before your silver immersion boards start to oxidize and become unusable (or shouldn't be useable :).

VS HASL in addition to even better shelf life they're going to be much flatter, so easier for assembly with BGA's QFNs etc. Silver immersion also has nice flatness.

Plus they look prettier over time since the gold stays shiny.

Here's some nice links on surface finish differences:

http://www.epectec.com/articles/pcb-surface-finish-advantages-and-disadvantages.html http://www.multicircuits.com/pcb/tech/surface_finishes.html

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  • \$\begingroup\$ Oh and cost I guess I should say would go in order, Gold ENIG, Immersion Silver, Maybe white tin?, then HASL. \$\endgroup\$ – Some Hardware Guy Dec 22 '14 at 21:01

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