PCB Stiffeners Impact the Reliability of Through-Hole Components

The rigidity of a circuit board plays an important role in its ability to withstand mechanical stresses. A stiffened board is able to avert damage or failure during installation, handling, and normal operation by reducing the impact of flexing and vibration. The most effective way to achieve this rigidity is through the use of a PCB stiffener. Stiffeners are typically made of either FR4 glass epoxy or polyimide and have various thicknesses to suit different requirements. They are most commonly attached to the flex PCB through an adhesive or using mechanical anchors. Often they are designed to be thermally matched with the PCB laminate to prevent a mismatch of coefficients of expansion that could cause stress and cracking.

Stiffeners are a key component of a flex PCB, allowing it to perform reliably in motion-sensitive applications. Their primary function is to limit flexing and provide stability during operation. They also reinforce connections, ports, and breakable circuit elements to protect them from excessive wear during connection, disconnection, and handling.

Typically, they are bonded to the flex PCB through an epoxy adhesive or through mechanical anchors. They should be properly sized and shaped to preserve flexibility in areas where they aren’t needed. They should also be anchored to the PCB in such a way as to avoid points of high stress concentration. In some cases, they may be embedded in the PCB laminate for a more durable attachment.

FR4 glass epoxy is a common choice for pcb stiffener due to its cost effectiveness and the ease of integrating it into the FPC’s substrate layer. Its rigidity is adequate for most applications and it is a good material for manufacturing and assembly. However, if the flex circuit needs to be exposed to harsh conditions, then a more resilient and temperature-resistant material like polyimide (PI) should be used.

How Do PCB Stiffeners Impact the Reliability of Through-Hole Components?

Another advantage of PI is its resilience to most chemicals. This can be a significant benefit when the flex circuit is required to endure chemical exposure during maintenance or repairs.

A major disadvantage of PI is its lower mechanical properties than FR4. This can cause it to be prone to cracking in large loads or in locations with stress concentrations. Its thermal conductivity is also lower than FR4, making it less suitable for a thermally matched stiffener.

Other material options for a stiffener include aluminum and stainless steel. These are more expensive, but they provide the structural integrity and capability required for some applications. For example, they are commonly used to meet the thickness requirement for zero insertion force (ZIF) connectors. They also offer additional resistance against abrasion and corrosion, which are critical for automotive or other motion-sensitive applications. Stiffeners are also commonly incorporated into metal core flex circuits to support the baseplate or other machined parts.