Prevent Delamination in Flexible PCB Boards
Delamination is a common problem in PCB fabrication and assembly. It is caused when layers of the PCB separate and break from one another, causing damage to the circuitry and halting the board’s functionality. The good news is that it’s possible to prevent delamination with proper PCB production techniques and quality control practices.
The most important factor in preventing delamination is to use high-grade materials. This includes both the base laminate and the conductive layer used for the copper traces. It’s also essential to ensure that the manufacturing process is up to par and the flex or rigid-flex circuit boards are properly baked before assembly. Even with these measures in place, delamination can occur for a number of reasons. Here are a few of the most common causes and how to mitigate them:
During the manufacturing process, if moisture isn’t removed from the flexible or rigid-flex circuit board, it can cause delamination. This can happen during reflow soldering during the assembly process or in the final heat treatments of the PCB, such as aqueous cleaning or UV curing. When the flexible pcb board is heated, the moisture that is entrapped in the polyimide or other insulating material can boil and expand, causing delamination of the layers. The best way to reduce the risk of this is to prebake the PCB before the assembly and soldering process. The bake out needs to be at a minimum above the boiling point of water, and for flex or rigid-flex circuits, this typically requires two hours in an oven.
How to Prevent Delamination in Flexible PCB Boards
Lastly, mechanical stresses that are outside of the design limits of the flex or rigid-flex PCB can also lead to delamination. This can occur during the manufacturing process, shipping and storage of the PCB. To minimize the risk, all personnel involved in handling and handling the PCB should be well-trained in the correct methods for handling the board. In addition, utilizing protective bags and padded pallets during transport and storage can help to further reduce the risk of mechanical stress.
While there isn’t much that can be done to prevent the occurrence of delamination in the final product, it is possible to mitigate this by ensuring that the PCBs are properly baked and subjected to a temperature profile that does not repeatedly exceed the glass transition (Tg) of the material. The Tg of the polyimide base laminate and the conductive layer are critical to this.
Regular inspection and testing can help to detect delamination in the early stages, so that it can be quickly identified and addressed. Nondestructive tests such as X-ray or thermography can identify the locations and severity of delamination, making it easier to address the issue before it becomes more severe. Modifications to the design and layout of the PCB can also help to reduce the chance of delamination. This can include altering the stackup structure, modifying the layers’ thicknesses, and incorporating additional reinforcing materials in areas of the PCB that are more likely to experience stress or strain.