PCB surface finishes

[joniengr081]

I just came to know that we need to tell PCB manufacturer about the surface finish which we don't define or include in the PCB layout in the design tools. What are these PCB surface finishes ? There are options for example, ENIG, ENEPIG, Leadfree HASL etc. Do they have any thing to do with signal and power integrity ? Is these finishes works only or applies only at top and bottom of the PCB ?

[jpanhalt]

The meanings are easily looked up.  ENEPIG is similar to electroless immersion gold (ENIG) except palladium instead of gold is used.
See here: https://www.pcbinternational.com/tech/enepig/

As for HASL, that's the cheapest and it works; however, I have read that for stencil printing it is easier to get reproducible results with the more even surfaces provided by immersion plating.  I have no experience with that.

[Jon_S]

You should be including this information in your ECAD data. It goes on the manufacturing layer, along with the other information such as dimensions, stack-up, and special features.

The surface finish solely determines manufacturability, at least at the level I work at. HDI or RF might be different.

HASL is generally the cheapest option, and it is suitable only for low-cost, high feature size PCBs. It is vaguely flat, has very few issues with storage or multiple reflows and is fine for 0805 size components or bigger, TQFP at a pinch. DFN/BGA is a really bad idea on HASL.

Immersion Tin, the next step up from HASL. It has good solderability, but storage can be a pain. Multiple reflow cycles can be a pain. Better than HASL if you treat it correctly.

Immersion Silver has excellent solderability, but storage/process is a serious issue because of oxidation. It is cheaper than gold finishes, but that is the only real selling point over them.

ENEPIG is an improved version of ENIG basically. If you are doing high-volume then you should look into the difference, otherwise these are the best all-round surface finish. Flat with excellent solderability, storage and multiple reflows are not a problem.

Organic Coatings (OSP etc...). These are very flat as they are just a thin film applied over the copper. Solderability is excellent, but if they get damaged, and even slight rubbing is enough, then you get oxidation and it all turns to worms. It can have issues with multiple reflow cycles.

Other finishes are more special purpose (hard gold for edge connectors etc...), you board house would likely be very happy to chat with you about the appropriate finish if you have questions about the best one for your particular application.

The finishes are only applied to the outer layers (usually anyway).

[ViaTech]

There are different kinds of surface finishes, such as HAL, ENIG, ENEPIG, immersion silver, immersion tin OSP, hard gold plating and soft gold plating. Surface finishes are usually applied on the top and bottom layers of PCB PADs to protect the pads from oxidation and contamination. It is also helpful for good soldering in PCB assembly. The most commonly used ones are HAL, ENIG, OSP and ENEPIG. HAL means Hot Air Leveling. In the process, tin melted and then levelled (blow) on the surface of the PCB by hot air. Immersion gold is short for ENIG; the full name is electroless nickel immersion gold, which means covering a thick layer of nickel and gold on the copper surface without a solder mask. A layer of organic compound is placed on the copper trace, which is free from the solder mask by chemical method. The full name of ENEPIG is Electroless Nickel Electroless Palladium Immersion Gold. It is developed above ENIG. The surface finish does not have much affection with signal and power integrity. But if there is tight impedance tolerance, it is better to use ENIG and ENEPIG surface finishes.

[wraper]

The meanings are easily looked up.  ENEPIG is similar to electroless immersion gold (ENIG) except palladium instead of gold is used.
See here: https://www.pcbinternational.com/tech/enepig/

As for HASL, that's the cheapest and it works; however, I have read that for stencil printing it is easier to get reproducible results with the more even surfaces provided by immersion plating.  I have no experience with that.

No, palladium layer is added between nickel and gold, while ENIG has gold directly on top of nickel.

HASL is generally the cheapest option, and it is suitable only for low-cost, high feature size PCBs. It is vaguely flat, has very few issues with storage or multiple reflows and is fine for 0805 size components or bigger, TQFP at a pinch. DFN/BGA is a really bad idea on HASL.

0805 is huge, 0603 can be used just fine with HASL, even 0402 as long as it was done properly with no huge solder blobs.

[wraper]

There are options for example, ENIG, ENEPIG, Leadfree HASL etc. Do they have any thing to do with signal and power integrity ? Is these finishes works only or applies only at top and bottom of the PCB ?

It only matters for very high frequency stuff when traces are not covered by solder resist. Look on spectrum analyzer teardown for example. As of power, surface finish layer is too thin to affect anything.

[Damperhead]

- OSP is great for consumer electronics. It is a viable option if all metal areas are soldered because the organic treatment wears off over time and no longer protects the bare copper -> oxidation.

- ENIG is an excellent all-rounder (when you take into account the passive-intermodulation (PIM) effect, Antennas etc.)

- ENEPIG is intended for Wire bonding applications. It should not be used in normal SMT electronics. Considerably more expensive than ENIG.

- My favorite is Immersion Tin, also works great with 0201 components. Nowadays, anti-whisker treatment is in use of Imm. Sn, so there is no need to worry about the whisker phenomenon characteristic of Sn.