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As the demand for miniature electronic devices has risen, the need for thin printed circuit boards (PCBs) with small components has also grown. Today, PCBs have become exceptionally compact and can be custom-made in varied configurations based on the requirement of the applications. However, compact-sized boards with several components and circuitry can lead to structural or curvature-based changes, overheating, and so on. These changes in curvature, twists, and bends result from PCB warpage which may occur due to thermal stress, inadequate circuit board manufacturing process, chemical, and other factors. If not handled properly, it may affect the paste printing quality, the formation of solder joints, and much more. Therefore, this warpage must be prevented so that PCBs function normally and have a good operational life. Would you like to know some preventative measures for the warpage of the circuit board? If that sounds yes, read this post to understand the PCB assembly warpage and its prevention in detail.
Warpage in the PCB assembly is defined as the unintended change in the circuit board geometry. Basically, the PCB should be precisely flat for the accurate placement of SMT components. This applies for flex boards too. The pick-and-place machine should release all the components at the required height above the circuit board. If the board has an altered shape or warpage, the machine experiences difficulties in maintaining exact height while releasing and placing the components on the board. This may result in low yield and additional rework during the assembly. Therefore, controlling the circuit board flatness is essential for preventing warpage in PCB assembly.
Warpage can be caused due to several reasons, and stress is one of them. PCB substrates experience frequent contraction and expansion during the production process. This is partly due to the heating and cooling processes involved. However, the difference between the expansion of substrates and that of the copper film is significant. This may cause unequal contraction and expansion between the two, leading the boards to warp. This can happen even at room temperature without a thermal process. The following are some common factors that influence warpage in the printed circuit boards:
Before getting into the possible solutions, it is also important to understand the impacts of warpage on circuit board assembly. The following section describes this in detail.
Some circuit board components come closer to the stencil, while others are further away in the case of warped PCBs. Hence, the solder paste may deposited more in the closer parts than the farther ones. Due to this uneven solder paste deposit, many issues arise. This may include solder bridges, open joints, head and pillow joints, and stretched joints.
There are many solutions that can prevent warpage in PCB assembly. Here are some of them.
One of the best ways to avoid warpage in PCB assembly is to balance copper amounts across all circuit board layers. This reduces the mismatch of the thermal expansion at room temperature and when it rises.
Next, extra care must be taken when using substrates across PCB layers. It is always a good practice to use a substrate of the same material and thickness in the bottom and top layers.
The temperature difference between the pallet and circuit board should be minimal.
Balancing copper density during panelization also helps minimize warpage in the PCB assembly.
All of the pointers mentioned above ensure that the PCB warpage is minimal or acceptable. If you are looking to assemble printed circuit boards (PCBs) for your industrial application, make sure you approach a reliable and highly experienced PCB manufacturer who understands and overcomes issues that can cause PCB warpage. With vast years of market presence, Creative Hi-Tech specializes in designing and manufacturing custom PCB assemblies for its clients. They comply with superior quality materials and components for PCBs sand comply with industry standards.