Printed Circuit Board (PCB) warpage refers to the phenomenon that the plane of the PCB is bent or deformed due to various reasons during the manufacturing, storage or use of the PCB. This deformation may be local or overall, and is usually manifested as the PCB no longer remaining flat. As we discuss in the previous blog "What is PCB Warping?", PCB Warpage have several adverse effects. But what causes this phenomenon?
Causes of PCB Warping
PCB Design
1. Unreasonable component layout
Component concentration distribution: If the components on the PCB are concentrated in a certain area, the weight and heat of the area will be concentrated, causing local stress to increase. In the case of temperature changes or mechanical vibrations, this local stress may cause the PCB to warp.
Asymmetric layout: If the layout of the PCB is asymmetric, it will cause uneven stress in different directions of the PCB. For example, when designing a double layer PCB, if there are more components on one side and relatively fewer on the other side, then during welding or use, the PCB may warp due to the different thermal expansion coefficients of the two sides.
2. Improper wiring design
Uneven distribution of copper foil: The copper foil on the PCB is an important part of the conductor, but if the copper foil is unevenly distributed, the thermal expansion coefficients of different areas of the PCB will be different. For example, a large area of copper foil will expand more when heated, while an area without copper foil or with less copper foil will expand less, resulting in a stress difference, causing the PCB to warp.
Unreasonable wiring direction: If the wiring direction on the PCB is inconsistent, it will cause different stresses in different directions. For example, when designing high-speed digital circuits, if the wiring direction is messy, different signal transmission delays and impedance changes may occur in different directions, causing uneven stress and PCB warping.
Suggested Reading：Large PCB Panel (≥500mm) Warpage Control
Material selection
1. Improper selection of substrate materials
Unmatched thermal expansion coefficient: Different substrate materials have different thermal expansion coefficients (CTE). If the thermal expansion coefficients of components, copper foil and substrate materials on the PCB do not match, different degrees of expansion and contraction will occur when the temperature changes, resulting in uneven stress and PCB warping.
Unsuitable material thickness and strength: The thickness and strength of the substrate material will also affect the warping of the PCB. If the substrate material is too thin or not strong enough, it is easy to deform and warp when subjected to external force or temperature changes. On the contrary, if the substrate material is too thick or too strong, it may make the PCB difficult to process during the manufacturing process and may also increase the risk of warping.
Unstable material quality: If the quality of the substrate material is unstable, there are differences in the performance of different batches of materials, which may also cause PCB warping. For example, some low-quality substrate materials may have internal defects, impurities and other problems, which may cause PCB warping during manufacturing or use.
2. Poor copper foil quality
Uneven copper foil thickness: If the PCB copper thickness is uneven, it will cause different thermal conductivity in different areas of the PCB, resulting in uneven temperature distribution, stress difference, and PCB warping.
Weak copper foil adhesion: If the adhesion between the copper foil and the substrate is not strong, the copper foil may peel off the substrate under conditions such as temperature changes or mechanical vibrations, causing PCB warping.
Production
1. Improper process parameter control
Inaccurate temperature control: In the manufacturing process of PCB, temperature is a very important parameter. For example, during the lamination process, if the temperature is too high or too low, it will cause uneven curing of the substrate material and adhesive, generate internal stress, and cause PCB warping. During the welding process, if the temperature curve is not set properly, it may also cause uneven heating of the PCB and cause warping.
Unreasonable pressure control: During lamination, drilling and other processes, a certain amount of pressure needs to be applied. If the pressure is too large or too small, it will cause uneven material distribution inside the PCB, resulting in stress differences, which will cause warping.
Improper time control: During the manufacturing process of the PCB, the time of each process link also needs to be strictly controlled. For example, during the curing process, if the time is too long or too short, it will cause incomplete or over-curing of the adhesive, resulting in internal stress and causing PCB warping.
2. Unreasonable production process
Repeated heating and moisture: During the production process of the PCB, if it experiences high temperature and high humidity environments many times, the performance of the PCB material will change, thereby increasing the risk of warping.
Improper processing sequence: During the manufacturing process of the PCB, different processing techniques have different sequence requirements. If the processing sequence is improper, it may cause uneven stress distribution inside the PCB, causing warping.
How PCB suppliers deal with warped PCBs
If a warped PCB is detected, the PCB supplier will usually take the following measures to deal with it:
1. Evaluate the degree of warping
First, conduct a comprehensive inspection and evaluation of the warped PCB to determine the degree and cause of the warping. You can use professional measuring equipment, such as a three-dimensional measuring instrument, a warpage measuring instrument, etc., to measure the warpage of the PCB and analyze the cause of the warping.
2. Take corrective measures
If the degree of warping is mild, you can try to take some corrective measures to restore the PCB to flatness. For example, the warped PCB can be corrected by heating and pressurizing. During the heating process, you can use equipment such as a hot air gun or an oven to heat the PCB to a certain temperature to soften the substrate material; then, apply appropriate pressure while heating to restore the PCB to flatness.
3. Scrap treatment
If the warping is serious and cannot be restored to flatness through corrective measures, or the corrected PCB still cannot meet the quality requirements, the supplier may scrap the PCB. At the same time, the supplier will conduct a comprehensive inspection and analysis of the production process to find out the root cause of the warping and take corresponding improvement measures to avoid similar problems from happening again.
4. Communicate and negotiate with customers
In the process of dealing with the warping problem, the supplier should communicate and negotiate with the customer in a timely manner, explain the cause and treatment of the problem to the customer, and provide corresponding solutions. For example, if the warped PCB affects the customer's production progress, the supplier can consider speeding up the production progress and providing the customer with a replacement PCB to reduce the customer's losses.
ALLPCB's strict control and treatment of PCB warping
ALLPCB is a professional PCB manufacturing company with a good reputation in the industry.
In the process of manufacturing PCBs, ALLPCB attaches great importance to the PCB warping problem and has taken strict control and quality inspection measures.
During the file review stage, ALLPCB engineers will carefully check the component layout and wiring design in the file. Once they find that there are concentrated distribution and asymmetric layout of components, uneven distribution of copper foil and unreasonable wiring direction, they will remind users that the PCB produced by this design has the risk of warping, and give reasonable suggestions for optimizing the design.
In terms of material selection, ALLPCB only selects high-quality and stable substrate materials and copper foil to ensure that the thermal expansion coefficient of the materials matches, the thickness and strength are appropriate, and the copper foil is of good quality.
During the production process, ALLPCB strictly controls the process parameters to ensure the accuracy of temperature, pressure and time, optimizes the production process, avoids repeated heating and moisture, and arranges the processing sequence reasonably. At the same time, ALLPCB has a professional quality inspection team to conduct comprehensive inspections on the completed PCBs, including warpage inspections, and has zero tolerance for PCB warpage.
In the event of a warped PCB board being delivered, the ALLPCB after-sales team will actively negotiate with the user to deal with the problem. They will quickly evaluate the warping situation, take corrections, replacements or other appropriate solutions, and do their best to reduce losses for users. At the same time, ALLPCB will also discuss with users how to improve product design and production processes to avoid similar problems from happening again. If users find any quality problems after receiving the PCB, they can contact our after-sales team central_support@allpcb.com, and we will deal with it as soon as possible.
Conclusion
In short, PCB warping is an issue that needs to be highly valued, which may have many adverse effects on the production and use of electronic products. Understanding the causes, effects and coping strategies of PCB warping is crucial to improving the quality and reliability of electronic products. As a professional PCB manufacturer, ALLPCB strictly controls and inspects PCB warping during the manufacturing process of PCBs, and has zero tolerance for PCB warping. At the same time, ALLPCB's after-sales team will also actively negotiate with users to deal with problems and do their best to reduce losses for users. I believe that with the efforts of ALLPCB, we can provide customers with more high-quality and reliable PCB products.