The "three properties" of PCB: manufacturability, testability, reliability

The "three properties" of PCB: manufacturability, testability, reliability

As an excellent PCB design engineer, you need to master some necessary design concepts so that you can design better boards. Today, let's learn about the "three properties" of PCBs in military standards: manufacturability, testability, and reliability.

Manufacturability of PCBs

Design for manufacturability (DFM) is to consider manufacturability and testability from the time of product development and design, so as to make a close connection between design and manufacturing, and achieve the purpose of one-time success from design to manufacturing. This is the most effective way to guarantee the quality of your PCB design.

The manufacturability of printed boards should mainly consider the following factors:

a) The processing capacity, technological level and assembly requirements of the equipment;

b) On the premise of satisfying the use, use less thin wire holes, special-shaped holes and slots;

c) The number of layers of the printed board should be minimized;

d) The overall dimensions should comply with the provisions of GB/T9315;

▲printed circuit board outline dimension series table (source: GB-T 9315-1988 printed circuit board outline dimension series)

e) If there are no special requirements, it is recommended to use FR-4 (GF) foil clad board.

Testability of PCBs

Design for Testability (DFT) is a technology that has emerged to meet the test requirements of the development of integrated circuits. The main task is to design a specific test circuit and adjust the structure of the circuit under test to improve the testability of the circuit, that is, Controllability and observability.

The testability requirements for printed boards are as follows:

a) The type and format of the test data shall meet the requirements of the test equipment;

b) Component holes and power (ground) lines (layers) should be easy to test;

c) When testing with a fixed probe, the test points should be arranged on the grid intersection, otherwise, the probe points should be set. Position holes should be set on both sides of the board in the X direction;

d) When testing with a moving probe, optical positioning marks should be set on the four corners of the board;

e) There should be no non-conductive material on all test points.

PCB reliability

Reliability, English is Reliability, and it is easy to understand from the literal meaning. We generally say "reliable", which means "reliable". Reliability is the nature and degree of reliability, which refers to whether users can trust the product when it is in use. , the ability and degree to which it can perform its functions and performance normally, accurately and stably.

There are many factors affecting the reliability of printed boards. Under the premise of satisfying the use, the following requirements should be considered:

a) Try to use common materials and popular processing techniques;

b) The design should be simple, symmetrical in structure and uniform in layout;

c) The number of layers of the printed board should be as small as possible, and the diameter and aperture of the connection pad, the width and spacing of the wires should be as large as possible;

d) The ratio of plate thickness to aperture should be as small as possible, generally not more than five to one.