How to Select Most Extensive Surface Finish in the PCB Manufacturing Process?

By | Date posted: | Last updated: August 14, 2020

When it comes to electronic assembly, surface finish of the PCB is one of the most crucial decisions that you could take. Surface finish, in turn has implications on a whole lot of issues, including but not limited to:

  • Process yield
  • Scrap Rate
  • Ability to test
  • Cost and more.

Selection of the surface finish must be done basis a whole range of factors. Sometimes the mistake that is made, is to go by costs alone. While in the short run you may seem to be saving costs, you could be in for a rude shock in the long term.

The 5 most popular surface finishes available today include:

  • Electroless Nickel or Immersion Gold
  • Immersion silver
  • Immersion Tin
  • Organic Solderability Preservative (OSP)
  • PB-free HASL

Each of them come with their own characteristic advantages to do with:

  • Solderability
  • Reliability
  • Shelf-life
  • Fabrication
  • Testability

When choosing a surface finish some of the aspects you must consider include:

  • Do you need direct wire bonding?
  • Is corrosion a concern for you?
  • Do you need wave solder?
  • Is shock or drop a concern area?
  • Do you require fine pitch assembly?
  • What kind of cost sensitivity do you have?

Let us look at the attributes of some of the surface finishes used in PCB Manufacturing, in some detail:

OSP

This surface finish is typically advisable to use when:

  • You need high volumes
  • When shock or drop is a concern
  • When you are looking for a cost-sensitive product
  • Fine pitch components are used.

OSP, however, isn’t recommended in cases where:

  • High yield ICT is required
  • Wire bonding is needed

Immersion Silver

This surface finish is used by PCB Manufacturers where:

  • High yield ICT is required
  • Cost sensitivity is important
  • Wire bonding is needed
  • Shock or drop is a concern area
  • Fine pitch components are used.

The limitations of Immersion Silver appear in:

  • Where corrosion failure is possible
  • Where the cosmetics of the finish are important to your overall scheme of things

Since tarnish is an issue, perception of quality often emerges as an issue with this surface finish.

Immersion Tin

It is recommended to use Immersion Tin Surface Finish in cases when:

  • Your requirement is high volume
  • You need high yield ICT
  • The look and feel of the finish is important to you
  • Cost is a concern area
  • PB shock is a concern

However, in cases where wire bonding is required or lead-free wave solder is needed it is best not to go in for this surface finish. It is also not a very popular choice with PCB Manufacturers, USA as it comes with a host of environmental and health concerns.

Electroless Nickel/Immersion Gold

The use is this surface finish is rampant where:

  • The look and feel of the finish is important
  • Wire bonding is needed
  • High yield ICT is required
  • Fine pitch components are used
  • You need a high shelf life

Clearly, however, this surface finish will not fit your bill if:

  • You need high volumes
  • Shock or drop is a concern area
  • You are looking at a low-cost finish

Pb-free HASL

This surface finish is the first choice for PCB Manufacturer California, where:

  • Cost sensitivity is a major concern
  • Look and feel of the finish is important.
  • High yield ICT is required.

In case of high volume requirements or where wire bonding is required, this isn’t a preferred surface finish.

As the above charts reveal, choosing the right finish is a fairly technical task. PCB manufacturers with experience and industry expertise are best suited to choose the right surface finish, which in turn has a lot of implication on the overall success or failure of the electronics assembly. Some of the industries where these finishes typically see a lot of application, include:

OSP

  • Computers
  • Handheld electronics

Immersion Silver

  • Consumer electronics

Immersion Tin

  • Aerospace
  • Peripheral components

Sometimes, however, the decision of the surface finish is taken erroneously based on:

  • The cheapest finish available
  • The one that is easily available from the supplier
  • The one that allows for testing
  • Where field failures are minimum

Each of these approaches can have long-term consequences and need to be avoided in isolation.

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