Understanding PCB Warpage and its Causes: A Comprehensive Guide
PCB warpage issue can cause major problems in the production process, leading to costly repairs and delays. If left uncorrected, warpage can even render the entire board unusable.
In this article, we’ll explore the root causes of PCB warpage and outline key steps for prevention and treatment. Read on to find out how you can protect your PCBs from warping and ensure a successful production process.
Table of Contents
What Causes PCB Warping?
PCB warpage is caused by the presence of imbalanced copper percentages in different layers of the board. This imbalance can be due to a variety of factors.
Weight of the circuit board itself
Weight is an important factor to consider when designing a circuit board. Not only can it cause problems with warpage, but it can also affect the performance of the board itself.
Heavy boards are more susceptible to flexing and bending, which can lead to shorts, breaks in traces, and other issues. This is why it’s important for designers to use lighter components where possible, such as thinner copper traces or smaller components.
Depth of V-Cut and the connecting strip
The depth of V-Cut and the connecting strip are two very important factors to consider when designing a circuit board. The V-Cut is the separation between two layers of the board, which helps ensure that there are no shorts or breaks in the traces. The connecting strip on the other hand, holds the two layers together. It’s important to get both of these elements right as they can affect not only performance but also durability.
When deciding on the depth of V-Cut, it should be based off of the height of components that will be placed on top of it. This ensures that there is enough clearance for any component leads so that they don’t come into contact with any traces underneath.
As for the connecting strip, this should be wide enough to provide sufficient strength and rigidity without making it too thick as this could cause warpage or reduce electrical performance.
Warpage caused during PCB processing
1. Incoming copper-clad laminate
Incoming copper-clad laminate is a key component of the printed circuit board (PCB) manufacturing process. It is important to ensure that the laminate you use is of high quality, so that it does not warp during production, resulting in poor electrical performance.
The first step to ensuring your incoming copper-clad laminate meets these standards is to check its CTE (coefficient of thermal expansion). A higher CTE rating indicates better resistance to warping caused by temperature changes.
The thickness and uniformity of the copper foil should also be checked as this can influence how evenly the layers are pressed together and ultimately affect electrical performance. It’s important to make sure that any exposed copper foil on the edges has been properly treated with soldermask or other protective measures against oxidation.
2. Pressing
Pressing is the process of laminating the copper-clad laminate to form a printed circuit board. This process is essential in order to ensure that all components are properly aligned and secured. It is also important to ensure that the pressing operation does not cause warpage of the PCBs.
Warpage can be caused by too much pressure or unevenly distributed pressure which can result in uneven boards and poor electrical performance.
3. Baking process of solder mask and characters
Baking is the process of curing the solder mask on printed circuit boards. The temperature of the oven has to be carefully controlled and monitored, since too high a temperature can cause warpage of the board.
The baking process is also important because overheating will cause the solder mask to shrink, leading to poor contact between components and unreliable performance. It is for this reason that it is essential to use an oven with adjustable settings so that you are able to find a setting that fits your specific needs. Additionally, it’s important to ensure that the boards aren’t exposed to strong winds during the baking process, as this can create additional warpage.
4. Hot-air solder leveling
Hot-air solder leveling is an important process in PCB production. It involves heating the board and then cooling it rapidly, which can cause warpage due to different materials and uneven structures. To minimize warpage during this process, it is important to keep the temperature of the tin furnace between 225℃ and 265℃ and the hot air temperature between 280℃ and 300℃.
Once the board has been taken out of the furnace, it should be immediately submerged in cold water for two minutes to reduce thermal stress. This will help ensure that your PCBs remain as flat and reliable as possible!
5. Storage
Storage is also the factor in causing warpage of your PCB. To ensure that your boards remain as flat and reliable as possible during storage, it is important to keep them away from sources of extreme heat or cold and make sure they are securely stacked.
You should avoid storing multiple different types of materials together since this can cause uneven stress on the boards. If possible, store your boards horizontally instead of vertically to reduce the chances of warpage due to gravity. If you find that your boards are still deforming during storage, you may want to consider using some kind of anti-warpage material such as foam or fabric to provide extra support.
How to Prevention of PCB warpage and deformation?
Preventing warpage and deformation of your printed circuit boards (PCBs) is essential for ensuring the quality of your products. Warpage can cause issues with components not fitting into sockets, incorrect contact between components, and other problems that can lead to costly delays and faulty products. Luckily, there are several steps you can take to reduce the chances of warpage in your PCBs.
1. Engineering design
Engineering design is the process of creating a product or system to solve a problem. It is an integral part of the development process and requires a thorough understanding of both the product and the problem it is intended to solve. Engineering design involves analyzing, planning, designing, prototyping, testing and refining your final product until it meets all of your specifications. By leveraging engineering design, you can create products that are more efficient and cost-effective than ever before.
At its core, engineering design follows a logical process which begins with research into the problem you’re trying to solve. You then analyze potential solutions, develop plans for prototyping those solutions, create prototypes for testing and finally refine your designs until they meet your desired performance goals. Through this iterative process, you can ensure that you develop products that meet customer needs while still being cost-effective.
2. Baking board before cutting
Baking a board before cutting is a crucial step in the development process, as it helps to ensure that your product meets all of your performance goals. The baking process removes moisture from the board and solidifies the resin, which helps to prevent warping. This step is typically done at 150 degrees Celsius for 8-10 hours, depending on the grade of the printed board and customer requirements.
For double-sided and multi-layer boards, baking can be done either before or after blanking – though some PCB manufacturer may opt out of this step altogether. If you’re unsure about whether or not baking should be part of your production process, it’s best to research thoroughly and make an informed decision based on your specific needs.
3. The latitude and longitude of the prepreg
The latitude and longitude of a prepreg are important factors to consider when manufacturing a printed circuit board. It’s essential that the warp and weft directions of the prepreg are distinguished, otherwise it can cause warpage in the finished product. To make sure you’re getting it right, it’s important to understand how to identify the warp and weft directions of your prepreg.
For rolled prepregs, the rolling direction is considered to be the warp direction while the width direction is considered to be the weft direction. For copper foil boards, on the other hand, the long side is typically considered to be the weft direction while the short side is usually considered to be the warp direction. If you’re not sure which way your prepreg should run, then it’s best to check with your manufacturer or supplier first before moving forward with any production processes.
4. Stress relief after lamination
Stress relief after lamination is an important part of ensuring that your printed circuit board is free of warpage and other defects. After the multi-layer board has been hot-pressed and cold-pressed, it’s important to place it flat in an oven at 150 degrees Celsius for 4 hours to gradually release any stress in the board and fully cure the resin. This step can’t be skipped as it’ll help prevent warpage in your finished product.
5. The thin plate needs to be straightened during electroplating
During electroplating, it’s important to make sure that the thin plate is straightened. If not, warpage can occur after the board is plated and it can be difficult to remedy. To do this, special clamping rollers are used to clamp the entire flybys down after the thin plate is placed on it. Then a round stick is used to string the rollers together and straighten all of the plates. This helps ensure that after electroplating a copper layer of 20-30 microns, there won’t be any bending or warping in your final product.
It’s essential to take this extra step during production as it’ll help prevent warpage and make sure that your performance goals for your product will be met. Plus, if you’re using an oven for stress relief before plating, make sure it’s calibrated correctly – otherwise, you could end up with warped boards! By following these simple steps during production, you can have peace of mind knowing that your board won’t warp or bend in the future.
6. Cooling of the board after hot air leveling
After the hot air leveling, it’s important to properly cool your board. When a printed circuit board is taken out of the solder bath, it should be placed on a flat marble or steel surface for natural cooling. This helps prevent any warping that can occur due to the high temperatures of the soldering process. If cold water is used to cool the board immediately after hot air leveling, warpage may occur in certain types of boards due to the hot and cold impact. This could cause twisted, layered, or blistered warpage in your boards if you’re not careful.
The best way to avoid this issue is by allowing your board to naturally cool before post-processing. Doing this will ensure that your finished product meets all performance goals and does not warp or bend when exposed to environmental stressors. So, remember – when taking PCBs out of a hot air levelling machine, don’t forget about cooling them off properly!
7. Treatment of warped board
Warpage is an unfortunate problem that can occur when printed circuit boards are exposed to extreme temperatures. If your PCB has been warped, all is not lost! There are a few treatments you can use to help straighten it out.
One of the most effective treatments for warpage is oven baking. This process involves placing the board in an oven at 150 degrees Celsius under heavy pressure for 3-6 hours, followed by natural cooling under heavy pressure. This helps relieve some of the stress on the board and keeps it from warping further. In addition, this treatment often helps save part of the board that could otherwise have been scrapped due to warpage.
Another option is to use hot air leveling to correct any warpage in the board. This process involves using hot air jets over a flat surface to gently level out any uneven surfaces or bumps on the board. While not as effective as oven baking, hot air leveling can be used in some cases to help straighten out warped boards and make them functional again.
FAQs
What is acceptable PCB warpage?
Acceptable PCB Board warpage depends on the specific application and the size of the PCB. Smaller PCBs can tolerate less warpage than larger ones. A typical industry standard for maximum acceptable warpage of a PCB is around 0.75% of the PCB length for a single-sided PCB and 1.5% of the PCB length for a double-sided PCB.
For more advanced applications such as high-speed circuit designs or surface-mount technology, PCB warpage should be minimized as much as possible to avoid signal integrity issues and potential reliability concerns. It’s important to consider the specific requirements of the PCB design and consult with a qualified manufacturer or designer to ensure the appropriate level of warpage tolerance for your specific needs.
How much can a PCB bend?
The amount a PCB can bend, or flex depends on several factors, including the thickness and material of the board, the size and placement of components, and the required application. Generally, flexible PCBs can bend or flex up to 180 degrees, while rigid PCBs have limited or no flexibility.
It is important to note that excessive bending or flexing can cause stress to the board, potentially leading to damage over time. Therefore, it is important to consider the intended use and environment of the PCB when determining the appropriate amount of flexibility.
How do you straighten warped PCB?
There have several methods that you can straighten warped PCB board, including heating, clamping, pressing, or using a vacuum chuck. One common approach is to use a reflow oven, which is designed to apply heat uniformly and can help relax the PCB and straighten it.
Another option is to clamp the PCB in a fixture or press with an applied force until it is straightened. Additionally, a vacuum chuck can be used to hold the PCB flat while it is being worked on. It is important to be careful when straightening a warped PCB as excessive force or heat can damage the board or the components on it.
How is PCB warpage measured?
PCB warpage is measured using various techniques such as shadow moiré, fringe projection, interferometry, and strain gauges.
Shadow moiré and fringe projection techniques use light patterns to measure the deformation of a surface. Interferometry measures the phase change of light waves passing through an object to determine the surface shape. Strain gauges are specifically designed to measure deformations in materials using the electrical resistance changes due to the applied pressure.
These methods provide accurate and reliable results to determine the degree of warpage and ensure the performance of the PCB.
Summary
Warpage is a common issue for printed circuit boards that can be caused by extreme temperatures. Thankfully, there are treatments available to help straighten out warped boards and make them functional again. Oven baking is the most effective way to treat warpage, as it helps relieve stress on the board and keeps it from warping further. Hot air leveling can also be used in some cases to help level out any uneven surfaces or bumps on the board.
No matter which method you choose, it’s important to take proper care when treating your warped PCBs so they don’t warp further or become damaged beyond repair. With patience and attention to detail, you can restore your boards back into working order with these treatments!
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