The surface finishes are important for a printed circuit board because they protect the board from oxidation. Along with making the boards resistant to corrosion, the surface finishes also help enhance the look of the PCBs. Different finishes have their own pros, cons, and uses. Are you intrigued to know these different types of finish options? What are their pros and cons? The following post is focused to answer these two questions. Read on to know more.
Surface Finishes- Their Types, Pros, and Cons
A printed circuit board can be applied with a variety of finishes, depending upon the application requirements. Here are a few most common types of surface finishes, along with the benefits that they offer. Also discussed are their disadvantages.
HASL (Hot Air Solder Leveling) / Lead Free HASL: HASL is one of the most commonly used, and most popular choices of surface finishes for several years. This finish has the capability to solder easily to the other surface. However, it has its own set of advantages and disadvantages, which are as follows:
Pros:
- Great Shelf Life
- Low Cost
- Re-workable
- Available Widely
Cons:
- Thermal Shock
- Uneven Surface
- Poor Wetting
- Poor Mechanical Strength
Immersion Silver: This is yet another commonly used surface finish, which is preferred by most manufacturers. These finishes are organic, as well as metallic in nature. It consists of OSP (Organic Solderability Preservative), which helps protect it from tarnishing. Here are some advantages of using this type of surface finish:
Pros:
- High Stability
- Complies with RoHS Directive
- Cost-effective
- Fine Pitch
- Easy Solderability
- Flat Coating
Cons:
- High Coefficient of Friction
- Sensitive to Electrical Testing
Immersion Gold: Commonly known as Electroless Nickel Immersion Gold, or ENIG, this surface finish has two layers of metallic coating. After the implementation of RoHS regulations, these surface finishes shot to popularity. This finish provides low contact resistance to the thin gold deposits. The following are some pros and cons of this finish:
Pros:
- Longer Shelf Life
- Flat Surface
- Lead-free
- Strong
- Good for PTH (Plated Through Hole)
- Suitable for Electric Test
Cons:
- Signal Loss
- Expensive
- Black Pad Syndrome
- Not Re-workable
- Complicated Process
OSP (Organic Solderability Preservative):This surface finish is most commonly used for copper pads. No toxins are introduced into the process, which makes this surface finish environmentally friendly. The finish provides an organometallic layer, with the help of a water-based organic compound. Just like any other finish type, the OSP also has its own merits, and demerits, which are as follows:
Pros:
- Repairable
- Lead-free
- Flat Surface
- Cost-effective
Cons:
- Sensitive
- Not Good for PTH
- Short Shelf Life
- Thickness Cannot be Measure
- Sensitive to Handling
ENEPIG (Nickel Palladium):ENEPIG stands for Electroless Nickel Electroless Palladium Immersion Gold. Commonly referred as Nickel Palladiuim, this surface finish is now being used increasingly in the printed circuit boards. This type of finish is ideal for aluminum and gold trace binding. The following are some advantages and disadvantages of choosing this as your finish option:
Pros:
- Long Storage Time
- Excellent Solderability
- Compatible with a Wide Variety of Surface Treatment Processes
- Cheaper than ENIG
Cons:
- Complex Process
- Hard to Solubilize
Immersion Tin:The chemical processes involved in the immersion coatings are generally costly. However, that required for immersion tin surface finish is least expensive of all. A chemical displacement reaction is used to deposit immersion tin on the surface of a printed circuit board. This type of finish is most commonly used for fine pitch products.
Pros:
- Cost-effective
- Lead-free
- Flat Surface
- Re-workable
- High Reliability
Cons:
- Tin Whiskers
- Sensitive to Handling
- Not Suitable for PTH (Plated Through Holes)
- Hard to Electric Test
Hard Gold: Hard gold finish, which is also sometimes referred as the hard electrolytic gold finish is commonly used over edge connector fingers and keypads, which are prone to extreme wear. In this finish, nickel, which acts as a barrier coat is plated by adding gold to it. It can be seen most commonly used on the game cartridges.
Pros:
- Longer Shelf Life
- Excellent Durability
- Lead-free
- Suitable for Electric Test
Cons:
- Higher Cost
- Demarcation
- Requires Additional Labor
- Requires Bus Plating
All these benefits offered by the finishes make them extremely important in the printed circuit board industry. Thus, a printed circuit board assembly is said to be complete, only after applying the proper surface finish. On the other hand, the cons of these finishes can make one think, whether to go with a particular finish type or not. This totally depends on the requirements of the application. Are you confused about which is the right surface finish for your PCB? Rigiflex is one among such few manufacturers, who can guide you in selecting the right type of surface finish for your PCBs, based on your application requirements.
