Warpage in PCB Assembly

What Are Top Causes of Warpage in PCB Assembly Process & Why Their Prevention Measures Needed!

Nov 16,2022

The demand for compact-sized and lightweight electronic devices has increased over the years. As a result, many components of these devices have become smaller, and printed circuit boards are one of them. These components feature high component density, and organizing all components on the PCB is one of the significant challenges faced by PCB designers. PCB warpage is one of the biggest concerns addressed by them. A warpage in PCB assembly or warping is a bent that occurs due to unbearable stress on a printed circuit board. This affects the overall functioning of a PCB by impacting the quality of paste printing and solder joints. Although experienced PCB designers follow the best practices of PCB design and assembly, warpage may still be a reality. If you have observed issues like open joints, stretched joints, head and pillow joints, solder bridges, etc., in your printed circuit boards, then it is probably due to the PCB warpage. What causes this warpage? Can it be prevented? Read this post to know the answers. 

What Causes Warpage in PCB Assembly?

Warpage in PCB assembly occurs due to the following reasons:

  • PCB Design: If a PCB design features unbalanced layers or misaligned fibers, then it may lead to unequal distribution of weight on the circuit board. This can force the board to bend upwards or downwards.
  • Thermal Expansion: Inappropriate heat application is the common cause of PCB warping. The thermal expansion between the copper layers affects the overall temperature of a PCB, thus resulting in unwanted bends.
  • Panelization: This is performed during PCB assembly to improve efficiency. Rails and outriggers are used during panelization. The outriggers are removed after the assembly, and printed circuit boards are depanelled to separate them. This causes the difference in copper densities of the outrigger and the board area, thereby causing warping. Sometimes using bigger and larger tabs than the panel can also cause warping. Additionally, if an imperfect plate is used during the paneling, it would affect the positioning of the boards. As a result, the assembly equipment may get stuck during the process and induce PCB warping. 
  • Thicker PCBs: Some PCB assemblers may create thicker PCBs than normal, depending on the application requirements. They may miss out on distressing the layers during the assembly. This would lead to warping after the assembly. 

Design Changes Done to Prevent Warpage in PCB Assembly

The causes that may lead to PCB warping cannot be eliminated from the PCB manufacturing process. However, warpage in PCB assembly can be prevented by implementing changes in the PCB design and assembly phase.

  • Copper weight must be balanced across PCB layers because it helps minimize the mismatch due to the coefficient of thermal expansion both at higher temperatures and room temperatures. 
  • Minimizing the temperature between the pallet and the PCB would help prevent warpage. Additionally, care must be taken to minimize the clearance between the edges of the PCB and the pallet. 
  • The difference between the copper densities in the outrigger areas and rails must be minimized to avoid warpage.
  • The PCB must be baked above its glass transition temperature, and this helps relieve the stress across the layers and minimize the chances of warpage.  

The above pointers will help PCB designers to minimize the effect of warpage during the PCB assembly. In addition, sourcing warpage-inspected PCBs from a trusted and reliable manufacturer can help you manufacture the best quality electronics that will lead to your business standards in the global market. Sierra Assembly Technology is one of the leading PCB assembly services providers that combine the best practices of PCB design and assembly with techniques to provide you with the quality PCB assemblies. The experts at the company will work with you closely to understand your requirements before deciding on the best designs and techniques to build performance-driven PCBs for your applications.