3 Ways to Prep for Your High-Reliability Class 3 Electronics Project

You’re an original equipment manufacturer (OEM) in need of an electronics contract manufacturer (ECM) to supply circuit boards for a product you haven’t built before. One of the first questions you need to ask is: “Should the boards meet Class 2 or Class 3 electronics standards?”

This is a question an experienced electronics contract manufacturer (ECM) should be able to help you answer. Think of this article as a GPS to getting a quote and a head start on the successful production of your high-reliability electronics project.

Is It Necessary for Your Project to Meet High-Reliability Electronics Standards?

The fact that you need to ask the question makes Class 1 standards irrelevant.

Class 3 is always the way to go if failure of your application could have catastrophic or life-threatening consequences. These products may include:

• Medical devices
• Military
• Aerospace

In fact, you might be asked to go beyond Class 3 to MIL-SPEC standards, as defined by the U.S. Department of Defense. These standards apply to almost all military and some aerospace applications.

However, Class 3 electronics (and above) cost more than their Class 2 counterparts, so you should have a discussion with an ECM before you make your decision. Just be sure the ECM has all the necessary certifications for Class 3 electronics production and can demonstrate experience in doing it.

Getting Ready for Class 3 Electronics Manufacturing Services

There are three main ways you can prepare to work with a contract electronics manufacturer at the Class 3 level. You should look at:

• Design strategies: What must you do to comply with Class 3 standards?
• Documentation: What do you need to provide to your contract electronics manufacturer to make your needs clear?
• Testing: What tests should be used on your product, and how are the results handled?
  
  

1. Design Considerations

Note that Class 2 and Class 3 projects share all but about 10% of their electronic components. The real difference between the two is how much work goes into manufacturing the boards.

In terms of Institute for Printed Circuits (IPC) guidelines, your design choices are less important than how your circuit boards are manufactured. IPC standards determine these factors, among others:

• Soldering
• Fastener tightness
• Placement of components
• Lacing of wiring harnesses

Specifications are tighter for Class 3 PCBs than for Class 2 PCBs. This includes how far parts can be off the pad (25% for Class 3, 50% for Class 2), which can affect the board’s service life and connection reliability. Coating standards are also much tighter for Class 3 boards.

Even given the tighter standards, you can still save money by working with your manufacturer to design for manufacturability. Your ECM can provide valuable suggestions about how to make the electronics manufacturing services less difficult and time-consuming -- and, in the end, less expensive.

2. Documentation Your ECM Needs From You

To ensure that you get an accurate price quote from your ECM, you need to supply your manufacturer with certain documentation as soon as possible. This documentation should include:

• Bill of Materials: The most important document you can provide, the BOM gives your ECM vital information, such as approved vendors, raw materials, and components.
  
  
• Assembly drawings: These should include board dimensions, thickness, layer number, part number, and most recent design revision.
  
  
• Gerber files: Used to develop stencils and placement of components, Gerber files apply to all image layers -- copper, silk screen, and solder mask.
  
  
• Approved custom item suppliers: If you’re using custom components, your manufacturer needs to know who supplies them. Most Class 3 projects require extensive record keeping.
• Testing, sampling, etc.: If you want these services, make sure your manufacturer has any applicable information, including programming, test requirements, and pick and place files. Also provide a product sample, if possible.
  
  
• Special processes: If your product requires special processes, you should provide the information. This includes: RoHS compliance, conformal coating, functional test, or in-circuit test.
  
  
• Agency certifications: Requirements to meet certain regulations could mean that your ECM must follow special component considerations. The ECM may even be audited by the agency involved. These agencies include, but are not limited to: UL (safety testing), the Food and Drug Administration, ATEX (for atmospheric explosives), and MSHA (Mine Safety and Health Administration).

3. Testing and Record Keeping

Class 3 electronics leave a long paper trail. Or at least they should.

Be sure your ECM has the full array of testing alternatives on hand with the personnel to make the best use of them. But as important as the testing itself is the documentation.

Extensive testing -- and the right tests -- help prevent problems from reaching the end user, and that can be crucial when you’re talking about Class 3, mission-critical electronics. Should something go wrong, documentary evidence of tests and inspections is essential. Any ECM worth its salt will keep inspection and test records for at least 10 years.

Most medical device makers require lot tracking. which allows PCB components to be tracked in case of an issue or recall. Make sure your ECM can accommodate this.

Say a PCB manufacturer makes 10,000 boards, but you find an issue with a certain component.  Your manufacturer should be able to reference a date code to find exactly when and where those shady components were placed  This could mean you only have to recall 20 boards instead of 10,000.

You Should Still Expect a Longer Process

This prep work should have you ready to successfully partner with an electronics manufacturing services provider. 

The best way to touch all the bases is to sit down with your EMS provider and work out the details well before designs have been finalized. Class 3 is touchy stuff, so even with this head start you should still account for extra testing and documentation in your lead time expectations. 

When lives are potentially at stake, it’s better to methodically put out a piece of high-reliability electronics than to rush it and fail spectacularly. Remember, that’s what you chose Class 3 specifications in the first place.

(Editor's Note: This blog was originally published in July 2019 and was updated in August 2021)