DFM is important in PCB design

Printed circuit boards (PCBs) are by far the most common method of assembling modern electronic circuits. Composed of a sandwich of insulating layer (or layers) and one or more copper conductor patterns, they can introduce various forms of errors into a circuit, particularly if the circuit is operating at either high precision or high speed. PCBs, then, act as “unseen” components wherever they are used in precision circuit designs. this article will introduce some associated with through-hole instrumentation design method can be made. It can greatly shorten the development, the production cycle, improve the design level, reduce the cost. Good design sometimes can save the PCB manufacturing cost.

A. typesetting and layout
At the design stage layout properly can avoid a lot of trouble in the process of manufacturing, and will be reduced to the minimum weld defects.
When making components layout should consider the following:
1) due to warping and weight is bigger size of the PCB in the production of transportation will be difficult, it needs to be fixed by special fixture, therefore should try to avoid using more than 23 panel of 30 cm. It is best to all of the board size control within two or three, and this helps to shorten the adjustment in the product replacement guide rail and turnover box width caused the downtime.
2) most of the automatic assembly equipment for PCB to set aside a certain edge easy clamping device. The scope of the clamping side should be 5 mm, in this range are not allowed to wash cloth components and welding plate.
3) as far as possible in the top surface of the board (component side) to carry on the wiring, PCB bottom (solder side) vulnerable to damage. Don't close to the edge of the board wiring, because the production process is conducted through the edge grasping, lines will be on the side of wave soldering equipment card claws or border transmitter damage.
4) for high pin number of devices such as seat or flat cable, wiring should use the oval pad instead of round to prevent in wave soldering tin bridge (figure 1).
5) as far as possible make the positioning hole spacing and the distance between the components, and its size according to instrumentation equipment to standardize and optimize the processing;
6) make positioning hole is also used as PCB mounting holes in the final product, which can reduce the production of drilling process.
7) for larger PCB, should be in the center of the plate to set aside a pathway to a wave soldering in a central location on the circuit board to support, to prevent the board prolapse and solder splash, helps the plate welding.
8) layout design should be considered when the needle bed measurability, can use the plane welding plate (leadless) with better pin connection, so that the online test nodes can be tested for all circuits.

B. component location and placed
1) the direction of array elements to consider when axial components should be parallel to each other, so that the axial thrust of installed in instrumentation, there is no need to rotate PCB for unnecessary movement and rotation will greatly reduce the speed of plug-in installed.
2) similar components on the board face emissions should be in the same way. For example makes all radial capacitor negative toward the right side of panel, make all dual in package (DIP) gap tag facing the same direction, and so on, so that we can accelerate the rate of instrumentation and easier to find errors. As shown in figure 2 shows, due to A plate adopted this approach, so make it easier to find A reverse capacitor, while B board find need more time.
3) dual in packaging components, connectors, and other high pin number elements of vertical orientation and the direction of a wave soldering, which reduces components of tin bridge between pins.

Mark element reference
4) Mark element reference operator (CRD) as well as the polarity, and the element is still visible after insertion, it is very helpful when checking and troubleshooting, and is also a good maintenance work.
5) to avoid the two sides are placed in the PCB components, because it can significantly increase assembly labor and time. If the components must be on the bottom should be close to a complete to prevent welding tape covered with stripping operation.
6) make elements evenly distributed on the PCB, in order to reduce the warp and help to make its uniform heat distribution in a wave soldering.
7) power devices should be evenly placed on the edge of the PCB or ventilated location inside the case;
8) valuable components don't wash cloth in the Angle of the PCB, edge, or close to the mounting holes, slots, makeup of cutting, gouges where whole pieces were missing and the place such as corner, above these position is high stress region of PCB, easy to cause solder joints and components of cracking or crack.

In the actual design, the design should be based on objective requirements and design conditions, the use of anti-electromagnetic interference reasonable measures, designed with good manufacturing performance of PCB board.