As a PCB design engineer, one must not only master the sketchboard skills, but also consider the factors of manufacturability design (DFM), which is an important part of PCB design. If DFM is not designed properly, there will be frequent problems. In this article, let’s take a look at common DFM problems and how to avoid them.
01: Selection and placement of components
Many designers minimize the use of in-line devices (THTs), or place in-line devices on the same side of the board. However, in-line devices are often unavoidable. In the case of a combination, if the in-line device is placed on the top and the patch device on the bottom, then all components should be as close together as possible. In some cases, this will affect single side wave soldering. In this case, more expensive welding processes, such as selective welding, are used.
02: Acute Angle
Sharp angles are sharp or strange angles on copper elements in a printed circuit board that can cause acid to build up during PCB creation. For this reason, PCB engineers need to avoid placing the wires in the pads at acute or strange angles, keeping the angles at 45 or 90 degrees near the pads.
03: Brass bars and isolated islands
Copper bars and islands are free floating copper in many flat layers, which can cause some serious problems in acid tanks. Tiny copper patches have been known to float off PCB panels and reach other etched areas on the panels, causing a short circuit.
Alternatively, if they are too big to float, it will become an antenna, which may cause noise and other interference within the board (since its copper is not grounded — it will act as a signal collector).
Note: There is no foolproof way to avoid copper bars and islands, we must check manually or using software.
04: A tin bridge is formed between the pins
Because the lines of the etching marks are very fine and the pin spacing is very close, the solder resistance layer is very important for PCB design. The absence of a solder barrier can result in large pieces of solder (especially between pins) during assembly, resulting in a short circuit. In addition, it reduces the corrosion protection of other copper in the outer layer.
To prevent these problems, the engineer must check the alignment between the pads to the etching lines and shapes, and the spacing between the solder resistance layers (sideband).
05: The radiator
The heat sink absorbs and radiates the heat of electronic devices through contact with metal substrates or thermal interface materials. If the opening of the solder layer in the radiator is too large, it may cause the device to float from the pad if the solder paste melts.
To prevent this, reduce the amount of solder paste placed on the radiator fin – do not use one large solder layer opening, instead, try to divide it into smaller solder layer openings. This will help ensure that the device does not float and collide with other components during baking, avoiding short circuits.
06: Package size in accordance with IPC standards
The pads in contact with the device on the PCB are very important in determining whether the device can be soldered reliably. If the package is designed to meet IPC standards, it ensures that the components are soldered correctly during production.
Low cost, high yield is the eternal pursuit of all companies. Through the implementation of DFM specification, the company’s resources can be effectively utilized to produce products with low cost, high quality and high efficiency. If the design of the product does not conform to the production characteristics of the company and the manufacturability is poor, it will cost more manpower, material resources and financial resources to achieve the purpose. At the same time, there is a heavy price to pay for delayed delivery, or even lost market.
DFM organically links the design department and the production department to achieve the purpose of information exchange, so that the design development and production preparation can be coordinated. Unified standard, easy to achieve automation, improve production efficiency. At the same time, it can also realize the standardization of production test equipment and reduce the repeated investment of production test equipment.
Nowadays, many enterprises are limited by the production scale, and a large amount of work needs external processing. Through the implementation of DFM, the manufacturing technology can be smoothly transferred between the processing unit and the processing unit, and the production can be organized quickly. The generality of manufacturability design enables enterprises to realize global production of products.
There is no proper DFM specification to control the design of the product, and such or other assembly problems are found in the late stage of product development, or even in the stage of mass production. At this time, it will undoubtedly increase the development cost and prolong the production cycle of the product if we want to correct them through design changes. Therefore, in addition to focusing on function first, DFM is also very important in new product development.
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