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Some PCB manufacturers, such as Eurocircuits or PCBWay, offer the choice of no conductor finish (vs ENIG, HASL, Immersion Tin, OSP or others). Since this option is not often chosen, it raises the price of small orders since the manufacturer cannot pool multiple orders.

In which conditions would this option make sense?

Could it be for a custom user-applied finish?

Could it be for situations where the surface finish would unpredictably augment the surface roughness, raising the line losses and raising the effective dielectric constant? This does not make sense since the copper will oxidize.

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  • \$\begingroup\$ When you say surface finish, do you mean options like HASL, OSP, or ENIG? \$\endgroup\$ – The Photon Jun 18 at 21:19
  • \$\begingroup\$ @ThePhoton yes. Most information online compares the trade-offs of HASL, ENIG, Immersion SIlver, etc., but disregard the use of no surface finish. \$\endgroup\$ – Rogozhin Jun 18 at 21:25
  • \$\begingroup\$ THere are many reasons for lack of soldermask but still use HASL or other oxide reducing finish for conductors. Did you mean no conductor finish or no dielectric finish? We designed and ordered brass PCB with no finish with dotted edge lines etched half way thru the brass with no FR4 into tin-plated RF boxes which we dipped and rinsed with tin plating ourselves for RF shields on LNA’s and VCO’s. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 18 at 23:05
  • \$\begingroup\$ @SunnyskyguyEE75 I edited the question. Thanks for the feedback! \$\endgroup\$ – Rogozhin Jun 18 at 23:29
  • \$\begingroup\$ As always yer welcome. So I assume you mean no finish for both soldermask and copper finish. .. dirt cheap and storage issues for copper in Nitrogen of used same day of up packaging in high volume for wave soldering. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 18 at 23:30
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Simple, low-cost circuits and where the order is so big that it can be grouped with itself?

It sounds like you're assuming that it raises the price because it can't be grouped rather than actually knowing that as a fact. I could be wrong, but I'm pretty sure PCB fabs don't group multiple commercial orders together.

I also don't think surface smoothness is the objective because where surface roughness matters, oxidation also matters so you would go with ENIG.

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    \$\begingroup\$ For really high frequency you might not want to use ENIG because nickel has some bizarre magnetic properties. \$\endgroup\$ – The Photon Jun 18 at 21:20
  • \$\begingroup\$ @ThePhoton I would assume in that case you would still not go bare copper but use an OSP finish instead? \$\endgroup\$ – DKNguyen Jun 18 at 21:25
  • \$\begingroup\$ @DK typically solder mask over bare copper (But then solder mask has its own issues) \$\endgroup\$ – The Photon Jun 18 at 21:32
  • \$\begingroup\$ That last statement wasn't really coherent with the topic at hand...was it? Bare copper under the solder mask, and surface finish (HASL, ENIG, OSP, or apparently bare copper as the OP asked) over the exposed pads which have no solder mask. \$\endgroup\$ – DKNguyen Jun 18 at 21:36
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In which conditions would this option make sense?

Cost, gold costs more. It used to be that the costs were much more for PCB's so any way to save money was a good idea. In my case I do have to worry about surface finish because it contributes to thermocouple effects (you're basically building a poor thermocouple with all of these layers of metal from pin to pad). For low level measurements it makes a difference.

Copper on copper makes up for a good connection if you need it (very little thermocoupling going on).

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  • \$\begingroup\$ Wouldn't you still go OSP rather than bare copper though if you wanted copper-copper connections or to save $$$ on gold? \$\endgroup\$ – DKNguyen Jun 18 at 21:28
  • \$\begingroup\$ If I wanted to not worry about thermocouple effects, I'd go with copper on copper. And use some deoxit in between. Usually I only do this on the connections that I need and put a keepout layer, not blanket the whole board with no surface finish. \$\endgroup\$ – Voltage Spike Jun 18 at 21:31
  • \$\begingroup\$ Back in the day, everything, surface finish and silkscreen had a substantial cost, some boards were made without \$\endgroup\$ – Voltage Spike Jun 18 at 21:32
  • \$\begingroup\$ Ah. I see. It sounded like you blanketed (or rather did not blanket) the entire board in bare copper. \$\endgroup\$ – DKNguyen Jun 18 at 21:33
  • \$\begingroup\$ My senior project, I got a board with bare copper because it was cheaper. \$\endgroup\$ – Voltage Spike Jun 18 at 21:46

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