What is the reason for PCB delamination and foaming? How to prevent PCB ink foaming?

ONESEINE PCB/What is the reason for PCB delamination and foaming? How to prevent PCB ink foaming?

There are two types of quality issues with PCB blistering and delamination: one is blistering inside the board factory, and the other is blistering during SMT reflow soldering by customers.

Let's first talk about the first type, which is the discovery of layered bubbles in the board factory:

1. Insufficient surface treatment before wiring, insufficient concentration of liquid medicine in the cylinder, and oxidation phenomenon on the board surface after treatment are the main reasons for foaming.

2. There is water accumulation on the surface of the solder mask before welding

3. No rack inserted after development

4. When forming, the gong board burns the board, and the gong machine lifts the knife unevenly with the board

5. When spraying tin, the temperature is too high and the time is too long.

Layered foaming during customer use:

When dealing with such quality issues, Mr. Li mostly found that the delamination bubbles on the client side were mostly caused by plugins, high reflow soldering temperature, long tin immersion time, and uneven temperature. Most new employees are most prone to this negative phenomenon.

The above are some of the main reasons for delamination and blistering on PCB boards, as well as improper electroplating treatment. Therefore, delamination and blistering should be analyzed according to the corresponding quality.

PCB delamination and foaming (blistering) are primarily caused by trapped moisture, thermal stress, and poor lamination quality. When a PCB absorbs moisture from humid storage environments, the water inside the laminate or prepreg rapidly expands into steam during high-temperature processes like reflow soldering or wave soldering. This steam pressure forces the layers apart, creating visible blisters or delamination. Another major cause is coefficient of thermal expansion (CTE) mismatch between different materials—copper, FR4, and prepreg expand at different rates under heat, generating internal shear stress that weakens layer bonding. Contamination on inner layers (such as residual oils, dust, or oxidation) before lamination also prevents proper resin adhesion. Using low-quality prepreg or exceeding the material’s glass transition temperature (Tg) can accelerate failure. Additionally, excessive thermal cycling or lead-free soldering (which requires higher peak temperatures) can degrade the epoxy resin over time, leading to progressive delamination.

PCB ink foaming (bubbling of solder mask) is usually caused by poor surface preparation, air entrapment during printing, or incorrect curing. To prevent it, start with rigorous cleaning: scrub the board surface, apply chemical cleaning to remove oils and fingerprints, then bake the board at 80–100°C for 15–20 minutes to drive out surface moisture. During ink mixing, add a small amount of defoamer (such as silicone-based or non-silicone defoamer) to break air bubbles. Use vacuum defoaming equipment at -0.095 MPa for at least 30 minutes after stirring to remove trapped air from the ink. Control printing parameters: ensure uniform ink viscosity, proper squeegee pressure and speed, and avoid excessive mesh tension that can introduce air. Pre-drying (tack drying) before final curing should be performed at a lower temperature to allow bubbles to escape. Finally, ensure complete curing at the recommended temperature profile; under-cured ink will blister under heat, while over-curing can make the mask brittle and prone to cracking. Proper via handling is also critical—if a via is tented on both sides, trapped air inside the via may expand and blow the ink, so use vented vias or proper via filling.