Our recent blogs have focused on the role flexible printed circuit boards have played in the health care sector. Specifically, we’ve taken a closer look at the increasing popularity of health-related wearables, medical devices, and radio frequency identification technology. We addressed some of the design requirements that companies will need to address as they produce these devices, including the importance of leveraging flex PCBs.
In this article, we’ll answer the question: Which flex PCB manufacturing class fits your wearable, medical device, or RFID design? Making the right choice here is essential for ensuring the final product’s performance will meet all requirements and goals.
Three Performance Classes
The different performance classes for PCBs were established by IPC, the trade association devoted to connecting electronics industries. IPC-6011 categorized and created three flex classes. These classes are differentiated by the degree of testing and inspection that the PCBs must receive—the higher the quality standard, the higher the classification.
Class One is classified as general electronic products, such as computer peripherals, as a Sierra Circuits blog explains. Class Two flex PCBs are dedicated service electronic products, such as cameras and smartphones, while Class Three refers to high reliability electronic parts. This last category includes any items in which the devices require 100% reliability and accuracy at all times. Satellites are one key example.
“Medical devices typically demand Class Three quality.”
These classes have serious implications for wearable, medical device, and RFID designs. Most wearables, especially fitness wearables, and RFIDs likely require only Class Two or even Class One flex PCBs. Medical devices, on the other hand, are often life-critical, in which case they demand Class Three quality. After all, any risk of failure is not acceptable for a pacemaker or implanted glucose monitor.
Those are the distinctions in the abstract, but what about the actual differences between the three main manufacturing classes? As mentioned above, Class 2 boards need to meet higher quality standards than Class 1, and Class 3 is even more stringent. This translates into a number of quantitative differences. For a complete guide, please see IPC-A-600G.
Copper Plating Voids
Class 3 printed boards cannot have any evidence of voids in copper plating holes. For Class 2, a single void in any hole is acceptable so 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 1 flex PCBs can have up to three voids in any given hole, so long as 10 percent or fewer of the voids have holes and no void is more than 10 percent of the hole length. As with Class 2, the voids cannot be more than 90 degrees of the circumference.
Finished Coating Voids
There are similar stipulations when it comes to the finished 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. 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 degree of the circumference.
Adhesive Squeeze-Out for Land Area
Class 3 boards are only acceptable if there is a 0.05 mm solderable annular ring around the entirety of the circumference of the pad. For Class 2, 270 degrees of the circumference need to hit this standard. For Class 1, 240 degrees must have a solderable annular ring, with no size restrictions.
These relatively small distinctions determine not just the classification of circuit boards, but also their reliability and capabilities. To ensure that a given circuit design meets the right qualification, and that the flex PCBs produce uphold these standards, it’s imperative that designers work closely using industry-leading PCB design software, as well as a reputable manufacturer that can deliver products that perfectly match the submitted designs and requirements.
Want to learn more about flex PCBs? Download our flexible design guide!