Key cost drivers: Parylene versus liquid conformal coatings

Guest Author: Warren Boomer, Thin Film Partners

We all realize some conformal coatings like Parylene are considered high-performance solutions. The material has been in continuous use for at least 60 years and we’ve come to accept it as a superior alternative to the liquid conformal coatings.

Over the years, I’ve learned that micron-for-micron it exceeds most of the capabilities of the liquid chemistries. In almost every metric it surpasses acrylic, epoxy, urethane and silicone resins in performance.

However, in addition to better barrier protection, what sets it apart from the rest is price.

Parylene is a substantially more expensive conformal coating solution than all of the other four liquid coatings. Having worked with both types for many years, I have rarely seen an exception to the rule.

Customers often ask me why does a film of 5 microns cost more than one that’s 50 microns or more?

They often get a partial explanation. Something on the order of, “It has better properties” or, “You get what you pay for”.

These are valid responses. But, I think there is a great deal more to be said in that domain.

Five factors that drive the cost of Parylene processing

Straight answers – no fluff. Indeed, Parylene is more expensive.

Here are five key points that set them apart.

  1. Process labor costs. Process preparation is relatively simple for liquid conformal coatings. For Parylene, preparation is much more labor intensive. Parts generally require cleaning, surface preparation and adhesion promotion.
  1. Masking Labor costs. Masking tends to be less complex for liquids unless dipping a circuit board. Masking for Parylene is typically more involved & complex due to trying to prevent a more invasive gas penetrating the parts.
  1. Capital equipment costs. They are much lower for liquid conformal coatings whether sprayed or dipped. Parylene requires a Chemical Vapor Deposition (CVD) process that is a much more expensive coating system.
  1. Process time costs. The liquid conformal coating process is quick and easy to apply (spray, dip or brush) with equipment. Minutes versus hours. Parylene is a complicated deposition process in a vacuum chamber and requires real skill all the time even after set up.
  1. Batch process costs. For liquid coatings the cost of process generally goes down with increased volume. It can be inline and continuous flow reducing the cost significantly. Parylene is a batch process.

In reality Parylene coating costs are really about labor time and equipment costs.

Unfortunately, Parylene processing has higher associated costs. Hence, we expect a difference in price.

But, it is possible to reduce the difference between the two processes.

How to reduce your Parylene costs

Design for Parylene coating

Designing the circuit board for Parylene processing is critical for reducing the cost of processing. Using the right components that are easy to mask, with the right spacing around them for tape or boots or fitting parts after coating all reduce costs are some of the many design rules identified to help save money.

The amount of operator intervention (labor) is easily the #1 factor impacting coating cost.

The time element involved in masking and de-masking all factor in. Labor can account for as much as 80% of coating cost.

Want to reduce these cost elements?

Design the circuit to reduce the labor costs.

Minimise the masking requirements

Parylene has high crevice penetration and the parts may need masking. Latex, Kapton tape and / or masking boots may be required.

Using the right tapes and the right reusable masking boots may reduce costs.

Also, using no-mask or “pre-masked” parts can help reduce cost of coating.

Custom fixturing, especially custom tooled racks, can impact on cost as well.

Choose the right Parylene material

This can be significant, depending on the material chosen. Choosing the right Parylene material is crucial since certain dimers are much more expensive than others.

Maximise the deposition rate

The coating forms on substrate at 2-3um/hour (for Parylene-C). Any faster can produce unwanted results – unreacted Parylene, poor adhesion, film discoloration, etc.

However, manipulating a few parameters, namely temperature and pressure, can step up the deposition rate, translating to increased throughput, additional runs and lower cost overall.

Optimise the chamber and batch size

More parts per batch effects cost. However, there is a “sweet spot”.

Too big a chamber slows run-time and requires more of the raw material (Dimer). In a “too large” chamber more Parylene is deposited on all its surfaces relative to the actual target area.

Too small and any economy of scale is compromised – producing higher cost per part.

A chamber dimension that is optimum for most coatings jobs ranges from 18-24” diameter, with similar height. If one needs to accommodate more, a collar with extensions can be used.

Optimise the time in chamber

Maximizing the deposition rate to allow for extra runs per device per day is important.

Perfecting the engineering process and other inputs will favorably impact cost by improving machine efficiency and throughput.

Choose the right Parylene partner

Parylene is a complex process. No one disputes this.

Not all coating services are equal. Choosing the right partner can affect your costs massively, both in cost per circuit board, and the amount of parts that are scrapped. 

Warren Boomer, Thin Film Partners

Warren boomerWarren is the founder of Thin Film Partners LLC, a company which offers end to end services in over 200 coating chemistries and virtually all platforms.

Find out more about Warren Boomer and Thin Film Partners.