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What Is PCB Immersion Silver Surface Finish?

One of the factors that distinguish printed circuit boards from one another is the kind of surface finish they have. There seem to be various types of surface finish for PCBs. In this article, we will focus on Immersion silver PCB, its definition, advantages, disadvantages, as well as how to locate the best manufacturers.

It’s no longer news that companies are now adopting safer, more efficient, cheaper ways to do PCB surface finish. For instance, lead is no longer encouraged for doing surface finishing for printed circuit boards in many regions around the globe. That has compelled manufacturers to explore other options, like immersion silver, immersion gold, immersion tin, hot air solder levelling, and OSP. Let us dive in deeper into what PCB immersion silver surface finish is really about.

Immersion Silver PCB

What is immersion silver PCB?

Before we define immersion silver PCB, let’s define a printed circuit board surface finish as that will help you understand the subject better. PCB surface finish refers to metallic joints established between bare copper and components in the PCB that are solderable. Having said that, the PCBs normally have a base surface that is copper. That surface can easily become oxidized if left without any protective coating. That is why it is necessary for printed circuit board surface finish to be in place before they are used for whatever purpose.

This simply refers to a special type of printed circuit board. In this PCB, the fabricator provides copper pads that are exposed with an immersion silver kind of surface finish. An immersion silver surface finish is not something that is new to companies that manufacture chips. It is used in such places to prepare aluminum wire bonds. Also used in other applications such as metallic done contact and EMI shielding, an immersion silver surface finish ensures a 5 to 18 micro inch thickness.

Immersion silver PCBs can be stored for more than a year if they are stored under the right conditions. The requirement is that anytime such boards are taken out of where they are stored, it is expected that they are used not later than 24hours.

This unique treatment process helps to fabricate a plate of between 5 and 18 micro inches on the surface of the copper, which is enough to prevent the copper for tarnishing. Instead, it makes it provides a conducive environment for other components to be soldered accordingly.

The way the immersion silver thing works is that it is based on a displacement reaction. Silver ions are meant to displace copper metals from the circuit board pad’s surface. At the initial stage, the fabricator roughens the copper surface a bit with a small etching solution. After which, an even layer of immersion silver begins to accumulate slowly on the surface. It should also be pointed out that the rate of deposition is always slow.

The rate of deposition is expected to be slow to enable the formation of a thick crystalline structure, where a silver layer of high density is eventually formed on the surface. Also, the slow rate at which the immersion silver surface finish is deposited to prevent any unwanted particle from forming in the process. The immersion silver finish used in this PCB finish usually lasts for a long time because of its long service life. In the succeeding section, we will discuss the benefits that come with using such a unique surface finish type.

Advantages of immersion silver PCB

We have already touched on some of the advantage of immersion silver PCB surface finish in the previous section. However, we will explain all the advantages in detail in this section.

  • Cost-effective – One of the benefits of using immersion silver PCB surface finish is that it is cheaper than some other options. It is about the best offer you can get if you are on a budget. This surface finish guarantees a great functional connection even though it is not as expensive as other options. The majority of users who prefer immersion silver do so because of the low contact resistance and the flat surface it provides.
  • Solder spreads better – Silver spreading is a challenge for most surface finishes. But, with immersion silver, that challenge is conquered because the silver enables the solder to spread without any stress. The essence of solder spreading easily is that it creates a bond physically stronger.
  • Environmentally friendly – This happens to be one of the top qualities of immersion silver when it comes to PCB finishes. It is considered completely safe and harmless to the environment.
  • Used multiple times – An immersion silver PCB surface finish can also be used multiple times regarding more than one soldering reflows. You can do multiple soldering reflows and it will still look good.
  • Immunity to black pad – It is worth mentioning that immersion silver is inert to black pad interfacial fractures.
  • Used in most industries – Immersion silver can be used in several applications such as in communication systems, automobiles, and computer peripherals.
  • Excellent conductivity – This attribute of immersion silver is what makes it a perfect fit for high-speed signal designs.

Disadvantages of immersion silver PCB

To get a balanced and unbiased view of immersion silver PCB, let us look at some of the things that make it less appealing.

  • A new technology – Immersion silver PCB is a relatively new technology. As such, it has not been adopted as one would have expected.
  • Forms solder joint voids – This is one of the reasons immersion silver PCB manufacturer is still not high. The silver surface also tarnishes slowly with time. Whenever it is left without protection, environmental sulfur reacts with it, which leads to the formation of silver sulfide on the surface of the pad.

Those are just a couple of the downsides or shortcomings of immersion silver PCB. So, if you intend to patronize this sort of surface finish, please have these disadvantages at the back of your mind.

Immersion silver vs immersion gold (ENIG)

Immersion silver and immersion gold are two highly sought-after surface finish types in the printed circuit board industry. Their names may look alike but they are not exactly the same thing. Thousands of searches online show that clients are eager to know which one is the best. As such, this section will try to explain the two surface finish types.

First, you need to understand that immersion silver is like an upgrade of HASL while immersion gold is also denoted as ENIG. There are many reasons to believe that immersion gold is more environmentally friendly than immersion silver.

Secondly, people choose immersion gold over immersion silver because it requires lesser use of lead & emission flux gotten from fusing oil and flux.

Thirdly, immersion silver appears to be cheaper than immersion gold when dealing with boards with 2 layers. However, as you increase the number of layers, you would discover that both prices are almost the same.

Immersion silver has an adorable shelf life and incredible solderability. Immersion gold on the other hand, is excellent for resisting corrosion, perfect for soldering, longer shelf life, ideal for and bonding aluminium wire.

On paper, you can almost choose immersion gold over immersion silver right away. But, then they can both serve you and are considered as high-quality surface finish.

Immersion silver vs silver plating

The only notable difference between immersion silver and silver plating is that one is produced by an electrolytic process whereas the other creates the coating when silver is immersed in a special solution. In the world of printed circuit boards, it is okay to refer to it as immersion silver plating.

Conclusion

Do you seek a reliable and reputable immersion silver PCB factory that can help you with your needs? If yes, then look no further as we are an experienced immersion silver PCB manufacturer that knows a lot about PCB immersion silver surface finish. We deliver the best services in this regard for a competitive price.

Therefore, if you have any enquiries about PCB immersion silver surface finish, you can reach out to us. We will be glad to help out in any way we can.

FAQs

The thickness of Immersion Gold is generally 1-3uinch (1-3u”, or 0.025-0.075um). If there is no special requirement, the PCB manufacturer considers that the tolerance of the thickness of Immersion Gold is ±20%; to reduce the cost and discount the actual gold thickness by 20%. For example, the gold thickness of the finished PCB is required to be 1u”, and the minimum gold thickness of the finished PCB is 0.8u”.

No, the immersion gold used in PCB is not gold but nickel-gold alloy.

Standard PCB finishes are immersion gold, immersion silver, immersion thin, OSP, HASL, etc.

You can learn how to store PCBs and store PCBAs in this article.

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