Prevent Delamination in Flexible PCB Boards
There is no one-size-fits-all answer to this question, as delamination in flex PCB boards can be caused by a number of factors. However, implementing batch testing, using high-quality materials, and considering environmental factors during fabrication, assembly, and use can help mitigate the risk of delamination in your product.
Delamination in flexible pcb board can be caused by moisture, thermal expansion and contraction, or mechanical stress. Moisture is often the most common cause of flex PCB delamination, as it can cause the adhesive bond to weaken over time. This can be due to improper packaging or storage of a flex circuit board, or it may occur during the manufacturing process when the board is exposed to heat and humidity.
Thermal expansion and contraction can also lead to delamination in a flex circuit, particularly if the core and flex layers have mismatched coefficients of thermal expansion. The resulting stresses can strain the layers, causing them to separate from each other. To avoid this, it is important to use a rigid-flex design that combines core and flex layers with matching CTEs.
How Do You Prevent Delamination in Flexible PCB Boards?
Mechanical stress can also cause delamination in a flex circuit, especially if it is subjected to repeated bending or pressure beyond its design limits. This is why avoiding tight bends and proper handling techniques can help prevent delamination. Stiffeners can be added to selected areas of a flex circuit to increase its strength, although this option increases the cost and thickness of the finished product.
A pre-bake step can be used to remove any remaining humidity from the base materials and assembled flex circuit prior to soldering. This can dramatically reduce the chance of post-soldering delamination.
Another possible way to improve the durability of a flex circuit is to use a thinner copper layer. This will decrease its weight and resistance to bending, while still providing sufficient conductivity. In addition, wider trace widths can be used to reduce the likelihood of cracking during bending.
The choice of surface finish for a flex circuit is also critical, as it can impact its ability to withstand the effects of moisture and temperature. The most resilient finish is Electroless Nickel Immersion Gold (ENIG), which provides a thin, durable, solderable surface that will protect the copper from corrosion and moisture.
To reduce the possibility of delamination in your flex circuit, it is important to choose a quality fab house that will pay attention to these issues. They should ensure that the material used meets the required specifications and is fabricated using a controlled lamination process. They should also ensure that the reflow profile and reflow temperature are optimized to minimize the effects of thermal excursions.
Finally, they should utilize visual inspections, AOI, and reliability tests to catch defects like delamination as early as possible and correct them before they become an issue. By following these simple guidelines, you can greatly increase the durability and longevity of your flex circuit. Having to rework or scrap a swollen flex circuit can be costly, so it is important to do everything you can to prevent it from happening in the first place.
