Pcb Surface Finishes Advantages And Disadvantages

- Jan 10, 2017 -

 Listed below are some more common surface finishes used in PCB manufacturing.


HASL / Lead Free HASL

HASL is the predominant surface finish used in the industry. The process consists of immersing

circuit boards in a molten pot of a tin/lead alloy and then removing the excess solder by using '

air knives', which blow hot air across the surface of the board.

One of the unintended benefits of the HASL process is that it will expose the PCB to temperatures

up to 265°C which will identify any potential delamination issues well before any expensive

components are attached to the board.

Printed Circuit Board with HASL / Lead Free HASL Surface Finish

Advantages:

● Low Cost

● Widely Available

● Re-workable

● Excellent Shelf Life

Disadvantages:

● Uneven Surfaces

● Not Good for Fine Pitch

● Contains Lead (HASL)

● Thermal Shock

● Solder Bridging

● Plugged or Reduced PTH's (Plated Through Holes)


OSP / Entek

OSP (Organic Solderability Preservative) or anti-tarnish preserves the copper surface from

oxidation by applying a very thin protective layer of material over the exposed copper usually

using a conveyorized process.

It uses a water-based organic compound that selectively bonds to copper and provides an

organometallic layer that protects the copper prior to soldering. It's also extremely green

environmentally in comparison with the other common lead-free finishes, which suffer from either

being more toxic or substantially higher energy consumption.

Printed Circuit Board with OSP / Entek Surface Finish

Advantages:

● Flat Surface

● No Pb

● Simple Process

● Re-workable

● Cost Effective

Disadvantages:

● No Way to Measure Thickness

● Not Good for PTH (Plated Through Holes)

● Short Shelf Life

● Can Cause ICT Issues

● Exposed Cu on Final Assembly

● Handling Sensitive


Electroless Nickel Immersion Gold (ENIG)

ENIG is a two layer metallic coating of 2-8 μin Au over 120-240 μin Ni.The Nickel is the barrier

to the copper and is the surface to which the components are actually soldered to. The gold

protects the nickel during storage and also provides the low contact resistance required for the

thin gold deposits. ENIG is now arguably the most used finish in the PCB industry due the growth

and implentation of the regular 

Printed Circuit Board with Electroless Nickel Immersion Gold (ENIG) Surface Finish

Advantages:

● Flat Surface

● No Pb

● Good for PTH (Plated Through Holes)

● Long Shelf Life

Disadvantages:

● Expensive

● Not Re-workable

● Black Pad / Black Nickel

● Damage from ET

● Signal Loss (RF)

● Complicated Process

Gold – Hard Gold

Hard Electrolytic Gold consists of a layer of gold plated over a barrier coat of nickel. Hard

gold is extremely durable, and is most commonly applied to high-wear areas such as edge connector

fingers and keypads.

Unlike ENIG, its thickness can vary by controlling the duration of theplating cycle, although the

typical minimum values for fingers are 30 μin gold over 100 μin nickel for Class 1 and Class 2,

50 μin gold over 100 μin nickel for Class 3.

Hard gold is not generally applied to solderable areas, because of its high cost and its

relatively poor solderability. The maximum thickness that IPC considers to be solderable is 17.8

μin, so if this type of gold must be used on surfaces to be soldered, the recommended nominal

thickness should be about 5-10 utin

           Printed Circuit Board with Gold – Hard Gold Surface Finish

Advantages:

● Hard, Durable Surface

● No Pb

● Long Shelf Life

Disadvantages:

● Very Expensive

● Extra Processing / Labor Intensive

● Use of Resist / Tape

● Plating / Bus Bars required

● Demarcation

● Difficulty with Other Surface Finishes

● Etching Undercut can Lead to Slivering / Flaking

● Not Solderable Above 17 μin

● Finish Does Not Fully Encapsulate Trace Sidewalls, Except in Finger Areas


Conclusion

It is important to select the appropriate surface finish for your project by considering the

various options while factoring in performance requirements and material costs.

For an example, if you are looking for the lowest cost then Tin-Lead HASL might seem like a good

choice, but it is not suitable for RoHS-compliant products. If your product does require RoHS,

you might consider lead-free HASL. That is only if there are no fine pitch components, since

LFHASL cannot be applied perfectly flat. If your design needs to be RoHS compliant and does use

fine pitch components, then you'll need to select a flat, lead-free finish, such as Immersion

Silver or ENIG. Bear in mind that doing so will necessitate the use of more costly high

temperature laminate.

Unsure of what you will need? Consult with a PCB fabricator prior to you making a selection.

This will ensure that the combination of the surface finish and material will result in a

high-yielding, cost-effective design that will perform as expected.


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Della Zhang

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