Tips to Avoid Flex PCB Delamination During Reflow

When assembling electronic components onto Flexible Printed Circuit, it is sometimes encountered that the flexible printed circuit board may experience delamination after reflow soldering. This problem usually shows as bubbles, delamination or deformation, which seriously affects the reliability of the product. Most of these problems can usually be avoided by replacing materials and processes.

Causes of Flex PCB Delamination

Material Quality

If the bonding between polyimide, copper, and adhesive is weak, layers can separate under heat. You need to determine whether the issue comes from the adhesive layer or the coverlay film. Coverlay or adhesive films with low heat resistance are more likely to fail. 

Manufacturing Process Issues

If the lamination temperature or pressure is too low, the layers may not stick firmly.

When going through reflow, any trapped air or leftover chemicals can expand and cause bubbles.

Design Choices

Placing bend areas too close to solder pads makes them vulnerable.

Large copper areas expand unevenly if not designed with stress relief.

Reflow Soldering Profile

Heating too fast doesn’t allow gases to escape. 

Exceeding the material’s heat limit (Tg) increases the chance of delamination. 

Moisture in the PCB 

If a flexible PCB absorbs moisture during storage, it can vaporize during reflow and cause layers to lift.

How to Reduce the Risk Better Materials 

Choose high-temperature-resistant PI film or LCP materials. 

Smarter Lamination 

Apply proper vacuum lamination to remove trapped air. 

Adjust pressure and temperature for a stronger bond. 

Design Improvements 

Add openings in large copper areas to release stress. 

Keep soldering pads away from bending zones. 

Optimized Reflow Settings 

Use a smooth temperature ramp-up to reduce shock. 

Nitrogen reflow can also help improve soldering quality. 

Moisture Control 

Store PCBs in a dry cabinet to avoid moisture absorption. 

Pre-bake at low temperature (60°C for 0.5 hours) before soldering to remove hidden moisture inside the layers. This simple step prevents vapor expansion and significantly reduces the risk of delamination. 

Flex Plus Experience

At Flex Plus, we have also encountered issues with layer to layer delamination in flexible PCBs after reflow soldering. We successfully resolved these problems by carefully adjusting the material selection, lamination parameters, and reflow soldering temperature profile.

Our team focuses on: Using high-quality PI and copper to ensure strong bonding. 

Running strict lamination processes with vacuum technology. 

Providing DFM support to minimize risks. 

Recommending low-temperature baking before reflow for moisture-sensitive projects. This combination of material know-how and process control allows us to deliver flexible and rigid-flex PCBs that pass multiple reflow cycles without peeling or warping.

Final Thoughts

I think blistering is a big problem in flexible printed circuit boards, it has reliability risk. By working with an experienced flexible PCB partner like Flex Plus, you can avoid common pitfalls and make sure your flexible circuits perform well in every assembly stage.

Need flexible PCBs that survive reflow without delamination? Contact Flex Plus today and let’s talk about your project.