Regarding the deformation of the PCB board, it can be analyzed from the aspects of design, material, production process, etc. It is briefly explained here for your reference.

Design:

(1) Matching of expansion and contraction coefficients

Generally, a large area of copper foil is designed on the circuit board for grounding, and sometimes the Vcc layer is also designed with a large area of copper foil. When these large areas of copper foil cannot be evenly distributed on the same circuit board When it is on, it will cause the problem of uneven heat absorption and heat dissipation. Of course, the circuit board will also expand and contract with heat, but if the expansion and contraction cannot be matched, it will cause different stress changes and eventually lead to deformation. At this time, the board If the temperature has reached the Tg value, the board will begin to soften and, after curing, become permanently deformed.

(2) The connection points (vias, vias) of each layer on the circuit board limit the expansion and contraction of the board

Most of today's circuit boards are multi-layer boards, and there are rivet-like connection points (through holes, blind holes, buried holes) between layers. Where there are connection points, the thermal expansion and contraction of the board will be limited. The effect will also indirectly cause plate bending and plate warping.

(3) The design of V-cut will affect the amount of panel deformation

V-cut can easily become the culprit of the deformation of the PCB board caused by external force, because V-cut is to cut grooves on the original large sheet, so the place where V-cut is prone to deformation.

Material:

(1) Coefficient of thermal expansion (CTE) difference

PCB board, usually FR-4 copper clad laminate is the most plate, and FR-4 copper clad laminate is composed of copper foil and dielectric layer, while resin and glass fiber cloth constitute the dielectric layer. However, under normal circumstances, resin and glass fiber cloth are not distinguished on the CTE, but are considered as the dielectric layer.
Due to the different materials of the copper foil and the dielectric layer, their CTEs are naturally different, so the changes caused by the influence of temperature are also different. When this change is reflected in the deformation, the difference between the two is reflected in the deformation of the PCB board.

(2) Local differences in the material itself

The problems of the material itself are extremely complex, such as uneven thickness, and will not be discussed in depth here.

Production process:

The reasons for the deformation of the PCB board processing process are also very complex, which can be divided into thermal stress and mechanical stress. Among them, thermal stress is mainly generated in the pressing process, and mechanical stress is mainly generated in the process of stacking, handling and baking of plates. The following is a brief discussion in the order of the process:

(1) incoming copper clad laminate

Most of the copper clad laminates are double-sided, with symmetrical structure and no graphics. The CTE of copper foil and glass fiber cloth is almost the same, so there is almost no deformation caused by different CTEs during the lamination process. However, the size of the copper clad laminate press is large, and there are temperature differences in different areas of the hot plate, which will lead to slight differences in the curing speed and degree of resin in different areas during the lamination process. Local stresses due to differences in the curing process. Generally, this stress will maintain equilibrium after pressing, but will gradually release and deform in future processing.

(2) Press fit

The lamination process is the main process for generating thermal stress on multi-layer PCB boards. Similar to the lamination of CCL, due to the local stress caused by the difference in the curing process, the thermal stress of the PCB will be more difficult to eliminate than that of the CCL due to its thicker thickness, diverse pattern distribution, and more prepregs. The stress existing in the PCB board is released in the subsequent drilling, contouring, baking and other processes, resulting in the deformation of the board.

(3) Baking process of solder mask, characters, etc.

Since the solder mask inks cannot be stacked on each other when they are cured, the PCB boards will be placed vertically in the rack to bake the boards for curing. The solder mask temperature is about 150°C, and the boards are easily deformed under the action of their own weight or the strong wind of the oven.

(4) Hot air solder leveling

Usually, when the hot air solder is leveled, the temperature of the tin furnace is 225℃~265℃, the time is 3S-6S, and the hot air temperature is 280℃~300℃. When the solder is leveled, the board enters the tin furnace from room temperature, and within two minutes after it is released, the post-treatment water washing at room temperature is carried out. The entire hot air solder leveling process is a rapid heating and rapid cooling process. Due to the different materials of the circuit board and the uneven structure, thermal stress will inevitably occur in the process of cooling and heating, resulting in microscopic strain and overall deformation, resulting in warpage.

other aspects:

(1) Storage

The storage of PCB boards in the semi-finished product stage is generally inserted vertically into the shelf. The tightness of the shelf is not adjusted properly, or the boards are stacked during the storage process, which will cause mechanical deformation of the board. Especially for thin plates below 2.0mm, the impact is more serious.


(2) The weight of the circuit board itself will cause the board to dent and deform

Generally, the reflow oven will use a chain to drive the circuit board forward in the reflow oven, that is, the two sides of the board are used as fulcrums to support the whole board. If there are heavy parts on the board, or the size of the board is too large, It will show the phenomenon of depression in the middle due to the amount of its own species, resulting in plate bending.

NextPCB is committed to becoming one of the world's best manufacturers of high-reliability multi-layer boards, and will make unswerving efforts in this direction. We strictly control the design, materials, and production processes, only for the ultimate High-reliability PCB boards are delivered to you.

In the traditional way of the past, design and manufacturing were divided into upper and lower parts. Due to the lack of digital information synergy, problems were only discovered after the product was manufactured. This mode causes enterprises to repeat development, procurement of components, debugging, etc., and spend a lot of technical investment and capital in the process of new product introduction.

Based on the above problems, NextPCB has specially launched DFM manufacturability analysis software, which acts as a bridge in series between design and manufacturing, and provides inspection rules that meet industry standards for PCB design and manufacturing. A series of problems are presented in the form of data . Because NextPCB DFM software can find problems before manufacturing and provide efficient and reliable problem solving solutions, it can greatly increase efficiency and reduce costs for enterprises.

In addition, NextPCB has deployed intelligent and automated equipment in each production and manufacturing process. The whole process adopts the MES system to automatically collect, analyze, and warn of data, to bridge the information gap between the decision-making end and the production end, and to detect and process orders in a timely manner. Generate unqualified items in the process of production and shipment, reduce product defect rate, reduce costs, and achieve standardization and effectiveness in the production process.

If you have the production needs of PCB boards, please come to NextPCB Electronic Proofing experience, I believe you will not be disappointed!

About NextPCB

NextPCB provides one-stop solution for PCB manufacturing, components sourcing, PCB assembly and stencil manufacturing, involving consumer electronics, automotive, medical and military communications, electric power, industrial control and other fields. Our business covers 166 countries and regions around the world. Our company is headquartered in Futian New Generation Industrial Park, Shenzhen, China, and has a PCB prototype factory, a PCB mass production factory, two SMT factories and two component storage centers, meeting the various needs of customers from all over the world.

For more information, please contact:
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