In the processing of rigid flex circuit boards, a key difficulty is how to achieve effective pressing at the joints of the boards. At present, this is still an aspect that PCB manufacturers need to pay special attention to. Below, Capel will give you a detailed introduction to several points that need attention.
Rigid Flexible PCB Substrate and Prepreg Lamination: Key Considerations for Warpage Reduction and Thermal Stress Relief
Whether you are doing substrate lamination or simple prepreg lamination, attention to the warp and weft of the glass cloth is critical. Ignoring these factors may result in increased thermal stress and warpage. To ensure the highest quality results from the lamination process, attention must be paid to these aspects. Let’s delve into the meaning of warp and weft directions, and explore effective ways to relieve thermal stress and reduce warpage.
Substrate lamination and prepreg lamination are common techniques in manufacturing, especially in the production of printed circuit boards (PCBs), electronic components and composite materials. These methods involve bonding layers of material together to form a strong and functional end product. Among the many considerations for successful lamination, the orientation of the glass cloth in the warp and weft plays a key role.
Warp and weft refer to the two main directions of fibers in woven materials such as glass cloth. The warp direction generally runs parallel to the length of the roll, while the weft direction runs perpendicular to the warp. These orientations are critical because they determine the material’s mechanical properties, such as tensile strength and dimensional stability.
When it comes to substrate lamination or prepreg lamination, proper warp and weft alignment of the glass cloth is critical to maintaining the desired mechanical properties of the final product. Failure to properly align these orientations can result in compromised structural integrity and increased risk of warpage.
Thermal stress is another critical factor to consider during lamination. Thermal stress is the strain or deformation that occurs when a material is subjected to a change in temperature. It can lead to various problems including warping, delamination, and even mechanical failure of laminated structures.
In order to minimize thermal stress and ensure a successful lamination process, it is important to follow certain guidelines. First and foremost, ensure that glass cloth is stored and handled in a controlled temperature environment to minimize temperature differences between the material and the lamination process. This step helps reduce the risk of warping due to sudden thermal expansion or contraction.
In addition, controlled heating and cooling rates during lamination can further alleviate thermal stress. The technology enables the material to gradually adapt to temperature changes, minimizing the risk of warping or dimensional changes.
In some cases, it may be beneficial to employ a thermal stress relief process such as post-lamination curing. The process involves subjecting the laminated structure to controlled and gradual temperature changes to relieve any residual thermal stress. It helps reduce warpage, enhances dimensional stability and prolongs the life of laminated products.
In addition to these considerations, it is also critical to use quality materials and adhere to proper manufacturing techniques during the lamination process. Selection of high-quality glass cloth and compatible bonding materials ensures optimum performance and minimizes the risk of warping and thermal stress.
Additionally, employing accurate and reliable measurement techniques, such as laser profilometry or strain gauges, can provide valuable insights into the warpage and stress levels of laminated structures. Regular monitoring of these parameters allows timely adjustments and corrections where necessary to maintain the desired quality standards.
An important factor to consider when selecting the appropriate material for various applications is the thickness and hardness of the material.
This is especially true for rigid boards that need to be of a certain thickness and stiffness to ensure proper function and durability.
The flexible part of the rigid board is usually very thin and does not have any glass cloth. This makes it susceptible to environmental and thermal shocks. On the other hand, the rigid part of the board is expected to remain stable from such external factors.
If the rigid part of the board doesn’t have a certain thickness or stiffness, the difference in how it changes compared to the flexible part can become noticeable. This can cause severe warping during use, which can negatively affect the soldering process and the overall functionality of the board.
However, this difference may appear insignificant if the rigid part of the board has some degree of thickness or stiffness. Even if the flexible part changes, the overall flatness of the board will not be affected. This ensures that the board remains stable and reliable during soldering and use.
It is worth noting that while thickness and hardness are important, there are limits to ideal thickness. If the parts become too thick, not only will the board become heavy, but it will also be uneconomical. Finding the right balance between thickness, stiffness and weight is critical to ensuring optimum performance and cost-effectiveness.
Extensive experimentation has been performed to determine the ideal thickness for rigid boards. These experiments show that a thickness of 0.8 mm to 1.0 mm is more suitable. Within this range, the board reaches the desired level of thickness and stiffness while still maintaining an acceptable weight.
By choosing a rigid board with the appropriate thickness and hardness, manufacturers and users can ensure that the board will remain flat and stable even under varying conditions. This greatly improves the overall quality and reliability of the soldering process and the availability of the board.
Matters that should be paid attention to when machining and fit:
rigid flex circuit boards are a combination of flexible substrates and rigid boards. This combination combines the advantages of the two, which has both the flexibility of rigid materials and solidity. This unique ingredient requires specific processing technology to ensure the best performance.
When talking about the treatment of the flexible windows on these boards, milling is one of the common methods. Generally speaking, there are two methods for milling: either milling first, and then flexibly milling, or after completing all the previous processes and final molding, use laser cutting to remove waste. The choice of the two methods depends on the structure and thickness of the soft and hard combination board itself.
If the flexible window is first millted to ensure the milling accuracy is very important. Milling should be accurate, but not too small because it should not affect the welding process. To this end, engineers can prepare milling data and can pre -milling on the flexible window accordingly. Through this, deformation can be controlled, and the welding process is not affected.
On the other hand, if you choose not to milling the flexible window, laser cutting will play a role. Laser cutting is an effective way to remove flexible window waste. However, pay attention to the depth of laser cutting FR4. Need to optimize the suppression parameters appropriately to ensure the successful cutting of flexible windows.
In order to optimize the suppression parameters, the parameters used by referring to flexible substrates and rigid boards are beneficial. This comprehensive optimization can ensure that appropriate pressure is applied during layer pressure, thereby forming a good hard and hard combination board.
The above are the three aspects that need special attention when processing and pressing rigid flex circuit boards. If you have more questions about circuit boards, please feel free to consult us. Capel has accumulated 15 years of rich experience in the circuit board industry, and our technology in the field of rigid-flex boards is quite mature.
Post time: Aug-21-2023
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