Flex PCBs are widely used in medical devices and wearables as they offer some great advantages. The demand for fitness wearables and medical devices is expected to increase even more in the upcoming years. Choosing an appropriate flex PCB manufacturing class is essential to ensure all the necessary requirements are met.

In this article, we’ll go through the following points:

Before we talk about flex medical PCBs, let us have a look at the standard IPC classes

Three IPC classes

The different manufacturing classes for PCBs were established by IPC, the trade association devoted to connecting electronics industries. The higher the quality standard, the higher the classification.

IPC class 1

Class 1 PCBs are classified as general electronic products.

IPC class 2

Class 2 flex PCBs are used in electronic products, such as cameras and smartphones.

IPC class 3

Class 3 PCBs are used in high-reliability electronic parts. This category includes any item in which the devices require 100% reliability and accuracy at all times. For example, medical applications generally use class 3 flex PCBs.

To understand the difference between class 2 and class 3 standards, read our article IPC Class 2 VS Class 3: The Different Design Rules.


IPC Class 3 Design Guide

Copper plating guidelines for medical flex PCBs

As a PCB manufacturer or designer, it is important to know the difference between class 2 and class 3.  Most of the time, even if the end product only requires class 1, class 2 PCBs are produced to ensure better performance. Void standards are among the biggest differences between classes. In the further sections, we will have a look at the standards for copper plating voids and surface finish coating voids.

Plating copper through-holes or vias are necessary for multi-layer or double-sided PCBs. Class 3 PCBs cannot have any evidence of voids in copper plating holes. For class 2, a single void in any hole is acceptable as long as no more than 5 percent of holes have voids. No void is more than 5 percent of the hole length, and the void is less than 90 degrees of the circumference.

Class 3 flex PCBs copper plating standards

  • No voids are allowed in copper plating holes of class 3 PCB.

Copper plating class 3 flex PCB

Copper plating standard for class 3 PCB

Class 2 flex PCBs copper plating standards

  • No more than one void in any hole
  • Not more than 5% of the holes should have voids
  • Any void should not exceed 5% of the hole length

Copper plating class 2 flex PCBs

Copper plating standards for class 2 flex PCBs

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Flex PCB surface finish guidelines

There are similar stipulations when it comes to the surface finish coating.

  • Class 3 boards cannot have more than one void per hole, no more than 5 percent of holes can have voids, and the void cannot be more than 5 percent of the hole length.
  • For class 2, three voids per hole are acceptable, but all of the other requirements remain the same.
  • Class 1 boards are acceptable if they have five voids or fewer in any hole, 15 percent or fewer of the holes have voids, and no void is more than 10 percent of the hole length. For all three classes, the voids cannot be more than 90 degrees of the circumference.

These relatively small distinctions determine not just the classification of circuit boards, but also their reliability and capabilities. It should also be noted that flex PCBs that are used in medical devices should be manufactured as per the IPC class 3 standards. To ensure that a given circuit design meets the right qualification, it’s imperative that designers choose the right manufacturing class with the help of a reputable manufacturer that can deliver reliable products.

Want to learn more about flex PCBs? Download our Flex Design Guide!

Flex Design Guide

This post was first published on: Sierra Circuits