Types of PCB Finishes-Which one is right for you?
Being the significant motorized support and union between the electronic elements and of specific devices, a printed circuit board or PCB has to go through the varied procedure before getting completely ready. PCB surface finish is one of them that retain the board from external damage. Let’s excavate a little to get all your doubts and queries resolved.
PCB Surface Finish
PCB surface finish is a remarkable part of any copper-made printed circuit board that correctly assures electricity flow. These delicate parts impose extra care and protection so that they don’t get damaged or oxidized or corrosion.
A range of distinct surface finishes has made our life quite easy by acquainting several effective finishes for every kind of process. Whether you are in search of a low-cost surface finish or an expensive and durable one, you can easily get your hand in one of those.
Contemplating the budget, the weather, reliability, and re-workability, several varieties of PCB surface finishes in demand. All of these finishes are reasonably great at doing their job, safeguarding the internal substances of the PCB board from decomposition.
Types of PCB surface finish
As mentioned earlier, PCB surface finishes compel substantial limelight while designing the board. The surface finish is essential to boost the circuit board’s strength by covering the copper inside it.
The options are many that one can select according to their preference. Therefore, the categories of PCB surface finishes are enlisted down below:
- Hot Air Solder Leveling (HASL)
- Lead-free Hot Air Solder Leveling
- Immersion Tin (ISn)
- Immersion Silver (IAg)
- Electroless Nickel Immersion Gold (ENIG)
- Electrolytic Hard Gold
- Electrolytic Wire Bondable Gold
These are some distinguished Types of surface finish that are consumed for industrial usage. To decide which one can function satisfactorily for you, let’s look at the several properties of different PCB finishes.
Hot Air Solder Leveling (HASL)
Hot air solder leveling or HASL, the most inexpensive among all, is highly known for its extensive use in industrial purposes.
Although HASL has been the ultimate preference of manufacturers for ages, the impediments and boundaries of this PCB surface finish cannot be ignored. In this technique, plunged into the molten solder gunk, the PCB is razed off with an ‘air knife’ that slams hot air across the ground of the circuit board.
With a through-gap or bigger SMT elements, HASL tends to function adequately. Contrarily, SMT particles slighter than 0805 or SOIC are not suitable to conduct HASL.
Pros:
- Very cheap
- Enables huge operating windows
- Popular among manufactures for long-experience
- Prominent finish
- Great self-life
- Re-programmable
Cons:
- Unequal surface
- Variation in density
- Solder stretching
- Thermal consequence
- Not eligible for HDI commodities
- Comprises lead
- Underprivileged for PTH
Lead-Free HASL
Unlike the conventional HASL process, this one is exempt from Lead-Tin solder. It uses Copper-Tin, Nickle-Tin, or Copper-Tin-Nickle Germanium instead.
But, on the other hand, Lead-free HASL is not as exemplary as the normal HASL when it gets to the minor particles. For a minor component PCB, a little costly but a beneficial process, immersion covering is highly recommended.
Pros:
- Moderately cost-effective
- Enables huge operating windows
- Considerable thermal expeditions
- Outstanding solderability
Cons:
- Variation in density
- Stretching on fine grade
- Increased temperature for processing (265° C -275° C)
- Not adequate for small components
Immersion Tin (ISn)
For planer, back plans, press-fit, and fine pitch products, Immersion Tin is a perfect surface finish indeed. ISn shortly pertains to the ground of a PCB through chemical deportation. On the other hand, it is quite inexpensive than other PCB finishes like insertion silver, ENIG, etc.
Although ISn conserves the elementary copper from oxidation, yet its inter-metallic connection with the copper is tended to be a little complicated. Additionally, the dispersion of the Tin into the underlying copper can have a consequence on the execution of the finish.
Pros:
- Completely Lead-free
- Cost-effective
- Works well for planers
- Smoother surface finish
- Re-functional
- Eligible for BGA and fine elements
Cons:
- Extremely delicate to utilize
- Gloves are a must to deal with harms
- Tin whisker
- The ratio of density is arduous to assess
- Relatively lesser self-life
- Underprivileged for PTH
Immersion Silver (IAg)
IAg prospered a world spread endorsement throughout ages for its RoHS proclamation deferred impact, and it’s taken as a great resort of ENIG as this finish possesses a capability for a steady pack layer and fine pitch. Unlike the immersion Tin, IAg doesn’t counter with copper though, and it tends to contaminate when uncovered in a free aura.
However, it includes OSP that prevents IAg from a quick tarnishing giving it a self-life of max 12 months in general. Gold plating can be an option to prevent tarnishing as well. This is normally utilized to coat switches, aluminum cord sticking, and EMI shielding, etc.
Pros:
- Fine pitch
- Planer
- Lofty strength
- Mid-range cost
- Re-workable
- Alternative to ENIG
Cons:
- Quick tarnishing
- Not suitable for Ni-Au pins
- Compels extraordinary packaging
- Silver whiskering
Electroless Nickel Immersion Gold (ENIG)
Encompassing a delicate coating of gold over electroless nickel, ENIG has become a highly popular economic demand. This flimsy coating of gold ensures the preservation of the nickel during depository.
This is not only thick and durable but also has a larger self-life. Although it’s quite costly, its stability and long-lasting ability have fulfilled the exact necessities in the industrial field.
Pros:
- Strong and long-lasting
- Large self-life
- Softer surface
- Lead-free
- Considerable for PTH
Cons:
- Non-re-programmable
- So costly
- Black pad problem on BGA
Choose the right finish for your PCBs
Now, when you’ve explored a pile of PCB surface finish options, hopefully, you are prepared enough. Remember, selecting the accurate option is probably the most critical task as the aftermath is depended on it.
For readers who are still in a dilemma, consulting a professional PCB fabricator would be the only option open for you. Seek assistance and find out the most cost-effective, robust, and sustainable PCB surface finish.
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