Types of PCB Surface Finishes:
A PCB surface finish is a coating between coating and a bare PCB. There are two main reason for this coating:
- To protect copper form exposed Circuitry.
- To ensure proper solderability.
ECI technology offers different solder finishes such as HASL, OSP, Immersion and ENIG and selecting right kind is not an easy task. Especially when electronics industry is getting complex every day and regulations like RoHS and WEEE have changed industry standards.
There are number of criteria to consider before choosing right solder finish which will reflect in later sections.
- Lead free vs Leaded Process
- Component type
- Predictability
- Reworkability
- Cost
HASL and Lead free HASL.
For quite a long time HASL was one of the most popular surface finish decisions. However, over the years, manufacturers have understood its limitations. While this surface finish is less costly and robust, it leaves the uneven surface and not suitable for fine pitch components. Even though it comes in lead-free, there are other options that are more likely for the high-reliable product.
Pros:
- Low cost
- Repairable
Cons:
- Poor wetting
- Less suitable for PTH (Plated Through Hole)
- Uneven surface
- Not suitable for fine pitch component.
Immersion Tin:
Immersion Tin (ISn) is a very good surface finish for fine pitch and planar components. Also, very popular with press fit and backplanes, ISn has more pros that cons. It is very good at protecting copper from oxidization. However, it’s intermetallic relationship with copper can be a problem.
Pros:
- High reliability
- Cost effective
- Planar
- Lead-free
Cons:
- Tin wiskering
- Limited rework
- Handling concern
- Not good for PTH
Immersion Silver:
For this surface finish, its benefits outweigh its cost. It started getting popular when RoHS and WEEE standards took effect. This is a very good alternative to ENIG with fine pitch component. Immersion silver contains OSP prevent tarnishing but can be sensitive to contaminants both on the board and in air.
Pros:
- RoHS compliant
- Planar
- Good for fine pitch
- High stability
Cons:
- Silver wiskerings
- Tarnishing
- High friction
OSP (Organic Solderability Preservative)
OSP is organic and water-based surface finish. It bonds with copper and protect copper pads before soldering. OSP require low equipment maintenance, environment friendly and comes lead free. However, it can be very sensitive to handle and is not as robust as HASL.
Pros:
- Simple process
- Repairable
- Even surface
- Lead-free
Cons:
- Not good for PTH
- Short shelf life
- Sensitive
Electroless Nickel Immersion (ENIG)
ENIG is quickly becoming the most popular surface finish in the industry. ENIG is well suitable with majority of industry requirements such as lead-free and components like BGA and SOIC which needs even surface.
Pros:
- Even surface
- Robust
- Lead-free
- Good for PTH
Cons:
- Expensive
- Not good for rework
- Black pad syndrome
Need more help to choose right surface finish for your new product? Contact ECI technology for help!
