PCB delamination refers to the layers within the board separating, weakening the circuit board structure, and influencing performance. This defect commonly occurs during PCB manufacturing, assembly, or even on a finished bare PCB or a complete assembled PCBA, making it critical to find out what triggers it and how to prevent it. This blog will walk you through finding the main causes of PCB delamination and learn how to prevent it, ultimately improving board performance and avoiding costly rework.
What Are the Main Causes of PCB Delamination?
PCB delamination can be triggered by a single cause or a combination of factors. The two main causes are excess moisture and repeated thermal cycling. And, there are other causes as well.
1. Moisture Absorption Causes
Laminated materials are prone to absorbing moisture if not stored properly, such as when exposed to a humid environment. During PCB manufacturing, residual moisture in the laminate material is converted into steam during high-temperature processes, such as reflow or wave soldering. The resulting expansion may cause PCB delamination.
While designers may tend to reduce resin content to decrease moisture absorption, this is not a good solution. Insufficient resin can prevent the glass fibers from being adequately wetted during the laminate process. The spaces between the fibers cannot be filled, leaving voids or weak bonding areas within the board. Ultimately, PCB delamination is more likely to occur later.
2. Repeated Thermal Stress Causes
A PCB (Printed Circuit Board) consists of multiple copper and dielectric layers. These layers are permanently bonded through a high-pressure and high-temperature thermosetting lamination process. Thus, it’s susceptible to thermal stress.
Repeated thermal cycling during soldering or rework can easily lead to PCB delamination, especially when the materials used cannot withstand temperature changes. Even after PCB assembly, delamination can occur if the PCB continues to be subjected to thermal stress above its glass transition temperature.
Thermal stress-induced PCB delamination typically occurs in the inner layers and does not create bubbles or cracks in the surface layers. The incidence of delamination is increasing. This is largely due to the widespread use of high-temperature lead-free solders, which subject PCBs to greater thermal stress to comply with RoHS requirements.
3. Lamination Process Causes
Laminate is a key process in PCB manufacturing, and improper process control can easily lead to PCB delamination defects. Stress, temperature, and time are important factors that can affect the bonding strength.
The resin is hard to fill adequately with insufficient pressure, so the bonding layers tend to loosen. However, the excessive pressure may damage the inner circuit. Over-temperature may facilitate the resin to flow excessively, which can even lead to decomposition. This will decrease the bonding strength. In contrast, the low temperature may prevent the resin from melting completely, which can not create good bonding. If the lamination time is too short, it will also increase the risk of PCB delamination due to incomplete resin curing.
4. Material-Induced Causes
When inferior materials are used in PCBs, the chances of delamination are higher. The low-quality materials are more easily affected by environmental influences, thermal stress, and mechanical stress. Furthermore, it’s also important to choose the right type of material. For example, unsuitable FR-4 Tg material can cause PCB delamination and peeling. If the Tg is too low, it will soften and reduce the bond strength under thermal stress or reflow. When the Tg is too high, but the lamination process is not done properly, it will lead to poor adhesion.
5. Mechanical Stress Causes
In the PCB assembly process, physical stress (flex, bend, and others stress) may damage the board, leading to microcracks. These microcracks can propagate and eventually cause PCB delamination.
How Can PCB Delamination Be Prevented?
Once you understand the main causes of PCB delamination, half the problem is solved. Once delamination occurs, there are some measures. However, it’s hard to guarantee complete repair. Therefore, most PCB delamination measures focus on prevention.
Baking to Eliminate Moisture
Baking circuit boards before thermal processing is a common preventative measure. Moisture can easily be trapped between the dielectric and copper layers, leading to PCB delamination. Wave soldering processes last only a few seconds, while SMT reflow can last 60 to 120 seconds. This means moisture has more time to seep out, making delamination more likely.
The baking process heats the laminate to a high temperature and holds it for a longer period of time to remove moisture. When baking, bear the following points in mind:
- The baking temperature should be above the boiling point of water (100 degrees Celsius), typically 105 degrees Celsius.
- During baking, ensure sufficient clearance between PCBs to guarantee good airflow.
Manufacture and Store in a Dry Environment
Exposing circuit boards to a humid environment increases the risk of delamination. Manufacturers must ensure a water-free environment throughout the entire production process. If storing PCBs for extended periods, always keep them dry and store them in sealed containers.
Using High-Grade and Right Materials
High-performance FR4 has a higher glass transition temperature (Tg) than standard FR4. If the PCBs need to experience multiple soldering cycles or have suffered significant temperature variations during operation, a high Tg material should be the ideal option. This material is more suitable for lead-free processes and multiple thermal cycles. Moreover, the selection of materials (prepreg, copper foil, etc.) should comply with industry standards and design requirements.
Controlled Manufacturing Process
During manufacturing, verify the reflow soldering profile and wave soldering parameters to avoid PCB delamination due to excessive thermal stress. Optimize lamination parameters (temperature, time, and pressure) according to the PCB material properties and structure. Lastly, it’s also important to maintain the lamination equipment to achieve reliable accuracy and performance.
Work with a Reliable PCB Manufacturer
To prevent delamination, work with reliable suppliers with strict quality control and stable performance. The suppliers should be able to pass all necessary qualification requirements and meet your needs, such as providing the required material and passing your specified tests.
Wrap Up
PCB delamination is a complex problem and a serious defect that can occur at any stage of production and even during operation. It affects the performance, reliability, and long-term durability of PCBs. However, understanding its causes allows for effective preventative measures, significantly reducing the risk of delamination. Furthermore, choosing an experienced PCB manufacturer, such as MOKOPCB, helps ensure the PCB operates stably in harsh environments. For any questions or concerns regarding your upcoming project, please contact MOKOPCB for expert advice.
FAQs
- What is delamination in PCB?
It refers to the separation of layers within the circuit board.
- What are the common signs of PCB delamination?
When the delamination occurs, the solder mask layer may develop large areas of discoloration and bubbles. The PCB may warp, peel, or even cause electrical failure.
- What is the difference between delamination vsmeasling?
Delamination is the separation between PCB layers, a more serious structural problem. While measling refers to the appearance of white spots inside the fiberglass cloth. Its impact is relatively minor, but it may still weaken the mechanical strength.
- What tests are used to evaluate PCB delamination?
When PCB delamination first appears, it occurs within the board and is difficult to observe with the naked eye. By the time you notice bubbles on the board, the circuit board’s functionality is almost compromised. There are several testing methods available, including scanning acoustic microscopy (SAM), thermomechanical analysis (TMA), stress testing parameters, etc.
- Can PCB delamination be repaired?
It’s hard to repair severe delamination, but minor cases can sometimes be mitigated through the following basic steps:
- Locate the delaminated area with the naked eye.
- Clean the affected area to remove debris and contaminants.
- Subject the area to heat and pressure, re-bondingthe layers.
- Allow proper curing in a controlled environment.
- Test the PCB electrically and mechanically to confirm it meets the required specifications.
