Circuit Board Stiffener Improve the Reliability of Solder Joints
A circuit board stiffener provides added support for a flexible printed circuit board and can help prevent damage during handling, installation, and regular use. They also help to distribute shock force evenly across the circuit, reducing stress on solder joints and making them more durable.
The most common type of circuit board stiffener material is FR4. It’s made of a woven glass fabric impregnated with epoxy resin and has good insulation properties. It also has a high tolerance to heat, making it a great choice for applications in the electronics industry. FR4 is also readily available with quick delivery times, making it an affordable option for most projects.
Polyimide is another popular stiffener material. It’s similar to FR4, but has higher resistance to chemicals and better performance in a wider temperature range. Polyimide stiffeners can be used in high-temperature environments, such as those found in aerospace applications.
Can a Circuit Board Stiffener Improve the Reliability of Solder Joints?
Metal stiffeners, such as aluminum or stainless steel, are ideal for flex PCBs that require anti-corrosion features, robustness, and formability. They’re expensive, however, and require a longer turnaround time than FR4 or polyimide.
Depending on the application, the thickness of a circuit board stiffener can vary from 8 mil to 59 mil (0.008″-0.059″). The thicker the stiffener is, the more support it offers for the flexible circuit board. Stiffeners are typically attached to a flexible circuit with pressure sensitive adhesive or thermal bonding methods.
To ensure the best results, it’s important to choose a stiffener that matches the thickness of the circuit board. Stiffeners that are too thin will cause the board to bend at or near components and connectors, which can lead to solder joint failure. Stiffeners should also be sized to ensure they’re easily bonded to the PCB with appropriate alignment and bonding procedures.
When a stiffener is attached to a flex circuit, it’s important to follow proper inspection and curing procedures. The stiffener should be aligned properly with the PCB, and it should be bonded to the PCB with the correct amount of adhesive. It’s also crucial to follow recommended curing time and temperature guidelines for the specific adhesive used.
Stiffeners can also be used to meet thickness requirements for zero insertion force (ZIF) connectors. ZIF connectors require a certain thickness to clamp onto the circuit board, and stiffeners can be used to achieve that thickness.
The reliability of a solder joint depends on its strength and the number of cycles it can endure. While FE simulations and experiments have shown that the life of a solder joint is more than three-times higher when a stiffener is added to a flexible circuit, it’s important to note that these results are dependent on the specific flex PCB used. Therefore, a solder joint that survives 500 cycles on a standard circuit board may not be able to survive 500 drops on a flexible circuit with the same design and manufacturing processes.