PCB Delamination: Causes, Warning Signs, and Prevention

PCB delamination is a major problem during manufacture, storage, and use. This article aims to help you understand its causes, signs, and prevention methods. We will also explain how to repair a delaminated circuit board.

Key Takeaways

• Definition: The physical separation of a PCB’s internal layers, including insulating laminates and conductive copper foils.
• Possible Causes: Weakened bonding material, thermal stress, moisture ingress, CTE mismatch, and mechanical forces.
• Major Delamination Signs: Raised spots, lifted sections, gaps in the stack-up, and electrical issues.
• Prevention Measures: Design optimization, proper material selection, controlled manufacturing and assembly steps, rigorous testing.
• Repairability: While surface-level pad lifting can be fixed, internal structural delamination often renders the board scrap in high-reliability applications.

What is PCB Delamination?

PCB delamination is the physical separation of the bonded surfaces of a printed circuit board. The surfaces can be laminate material layers, such as those of an FR4 board, or conductive copper foil.

The separation affects the board electrically and structurally. It may break internal traces and cause open circuits or a loss of electrical continuity, or make the board less robust and shorten its lifespan.

The image above shows a delaminated circuit board. Note the raised surfaces, which indicate layers that are separated. The following section explains factors that can lead to a delaminated circuit board.

Common Causes of PCB Delamination

Why does a PCB delaminate? Separation typically happens when internal stresses exceed the bond strength of the materials.

1. Thermal Stress

Excess heat or temperature changes expand materials (including gases) within the PCB’s structure, leading to mechanical stress. It may also weaken the bonding material and increase the chances of layer separation.

2. Poor Lamination

Layer separation may also result from insufficient or poor-quality adhesive. The lack of bond strength makes the layers susceptible to delamination. The problem may also occur if the bonding material doesn’t cure properly.

3. Material Mismatch

A mismatch occurs when materials with different CTE values, such as copper and FR4, expand at different rates when heated. The difference produces forces that break the bonding material between the layers, forcing them apart.

4. Moisture Absorption

Moisture is a leading cause of layer separation on PCBs. It usually occurs if a board with trapped moisture gets exposed to heat. The moisture turns to vapor, expanding rapidly and triggering delamination.

5. Mechanical Stress

A PCB will also delaminate if subjected to mechanical forces during manufacturing, testing, or other operations. The forces include twisting, bending, and excessive vibrations. They break the bonds between layers.

Common Signs of PCB Delamination

Delamination in PCBs can show in various ways. Some signs are easy to spot, while some require thorough inspections. Here is how to tell if a circuit board has delaminated layers.

Blisters and Bubbles

Raised surfaces (blisters and bubbles) appear on the board. These mainly result from trapped moisture expanding in high temperatures and pushing layers. It may also occur as white spots on the board (measles).

Visible Gaps or Voids

There are gaps where the layers have separated in a multilayer circuit board. Inspections using Scanning Acoustic Microscopy (SAM) or micro-sectioning will also reveal internal voids. They indicate areas of trapped moisture or gases.

Cracks or Discolorations

The board shows cracks, especially around vias. The weakened areas may also be discolored. These are signs of layer separation that further inspections and testing can help to verify.

Board Warping

The board warps, revealing internal damage due to mechanical or other forces. The warped board may be challenging to work with, especially if the separation occurs before mounting components.

Electrical Issues

Connections break, causing electrical failures. The failures are intermittent or sustained, depending on the extent of damage. They may appear as short circuits or other signal and power issues during tests.

How to Prevent Delamination in PCB

PCB manufacturers prevent delamination by optimizing board design and controlling fabrication and assembly steps. They also implement proper handling methods to prevent damage. Let’s discuss each step.

Design and Material Selection

• Distributing copper uniformly to prevent unequal expansion.
• Incorporating thermal vias to remove heat from internal layers.
• Minimizing the use of vias and regulating their distribution.
• Choosing high-quality laminates and premium resins to bond the layers.
• Using stiffeners to reinforce flexible circuit boards.

Board Fabrication

• Removing all air when laminating the layers to prevent entrapment.
• Avoiding fabrication technologies that induce mechanical strain.
• Ensuring utmost cleanliness during lamination to avoid contamination.
• Employing proper curing and other measures that control the lamination process.
• Ensuring adequate resin content when bonding the layers for a robust stack-up.
• Producing prototypes and testing them to detect design mistakes.

Assembly and Handling

• Baking circuit boards (in accordance with J-STD-033 guidelines) to remove moisture before subjecting them to soldering heat.
• Controlling soldering profiles and reducing fluctuations through gradual ramping and cooling.
• Proper handling to prevent situations that cause physical damage to the board.
• Storing bare or assembled boards in controlled conditions to limit thermal, moisture, and other delamination causes.
• Conducting reliability testing to identify flaws that require correction before PCB assemblies leave the factory.

How is Delamination Detected in PCBs?

To detect separated layers, engineers may visually or optically inspect circuit boards. They may also use imaging technologies and micro-sectioning to examine internal structures or perform electrical tests.   

Visual/Optical Inspection: This method involves examining the boards to identify signs of layer separation, such as bubbles. The inspection may be manual, using the eyes, or automated with optical equipment.

Internal Imaging: It visualizes the board’s internal layers to detect separation using ultrasonic scanning (SAM) or thermal imaging.

Micro-Sectioning: Also called micro-section analysis, this technique involves cutting a cross-section of the board to reveal its internal structure for inspection and analysis.

Electrical Testing: A tester takes electrical measurements to detect delamination problems, such as cracked transmission lines and other conductive surfaces.

PCB Delamination Repair

Delamination compromises a circuit board’s structure and performance. In severe cases, it can make the PCB unsafe or unusable. While repair is not always helpful, you can fix layer separation using these methods.

Thermal Re-bonding: Using heat and pressure to stick the delaminated layers together and restore their bond. It only works if the separation is not severe and involves small layer sections.

Resin Injection: Reapplying resin, such as epoxy, to replace the weakened bonding material in the separated surfaces, then pressing them together under pressure. The resin is low-viscosity and is typically used to repair blisters. However, for multi-layer or high-reliability boards, this method often cannot restore the original dielectric properties, and the board is typically scrapped to ensure performance.

Replacing Damaged Pads and Traces: This method repairs surface-layer delamination. You remove broken traces or lifted pads and replace them with an adhesive-backed copper foil.

Conclusion

PCB delamination is a destructive but preventable problem. By eliminating the causes of layer separation, manufacturers can produce circuit boards that remain intact throughout manufacturing and application cycles.  

At Jamindo, we employ advanced vacuum lamination and strict moisture-control protocols to ensure the highest reliability. Contact our engineering team today to discuss your next project.