PCB Blog - Items to be checked after PCB wiring is completed

1. PCB board design inspection
The following checklist covers all aspects of the design cycle, with additional items for special: applications. General PCB board design drawing inspection items:
1) The circuit is analyzed or not, and the circuit is divided into basic units in order to smooth the signal;
2) Whether the circuit allows the use of short or isolated key leads;
3) Where must be shielded, whether it is effectively shielded;
4) Make full use of the basic grid graphics without;
5) Whether the size of the printed board is the size;
6) Whether to use the selected wire width and spacing as much as possible;
7) Whether the preferred pad size and hole size are used;
8) Whether the photographic plate and sketch are suitable;
9) Whether there are few jumper wires used; whether the jumper wires should pass through components and accessories;
10) Whether the letters are visible after assembly; whether their size and model are correct;
11) In order to prevent blistering, is the large area of copper foil opened?
12) Whether there is a tool positioning hole;

2. PCB board electrical characteristics inspection items
1) Whether the influence of wire resistance, inductance and capacitance has been analyzed; especially the influence of the key voltage drop to grounding;
2) Whether the spacing and shape of the wire accessories meet the insulation requirements;
3) Whether the insulation resistance value is controlled and specified at key points;
4) Whether the polarity is adequately identified;
5) The influence of wire spacing on leakage resistance and voltage was measured from the geometrical point of view;
6) Whether the medium that changes the surface coating has been identified;

3. PCB board physical characteristics inspection items
1) Whether all pads and their positions are suitable for final assembly;
2) Whether the assembled printed board can meet the shock and vibration power conditions;
3) What is the spacing of the specified standard components;
4) Whether the components that are not firmly installed or the heavier parts are fixed well;
5) Whether the heat dissipation and cooling of the heating element are correct; or whether it is isolated from the printed board and other thermal elements;
6) Whether the voltage divider and other multi-lead components are positioned correctly;
7) Component arrangement and orientation for easy inspection;
8) Whether all possible interference on the printed board and the entire printed board assembly has been eliminated;
9) Whether the size of the positioning hole is correct;
10) Whether the tolerance is complete and reasonable;
11) Control and sign off the physical properties of all coatings;
12) Whether the ratio of the diameter of the hole to the lead wire is within the acceptable range;

4. PCB board mechanical design factors
Although the printed board supports components mechanically, it cannot be used as a structural part of the entire device. On the edge of the printing plate, at least every 5 inches for a certain amount of support. The factors that must be considered in the selection and design of printed boards are as follows;
1) The structure of the printed board - size and shape.
2) The type of mechanical accessories and plugs (seats) required.
3) The adaptability of the circuit to other circuits and environmental conditions.
4) Consider mounting the printed board vertically or horizontally depending on factors such as heat and dust.
5) Some environmental factors that need special attention, such as heat dissipation, ventilation, shock, vibration, humidity. Dust, salt spray and radiation.
6) Degree of support.
7) Hold and fix.
8) Easy to take off.

5. Installation requirements for printed circuit boards
It should be supported at least within 1 inch of the three edge edges of the printed board. According to practical experience, the spacing of support points of printed boards with a thickness of 0.031-0.062 inches should be at least 4 inches; for printed boards with a thickness of more than 0.093 inches, the spacing of support points should be at least 4 inches. 5 inches. Taking this measure increases the rigidity of the printed board and destroys possible resonances of the printed board. A printed board usually has to consider the following factors before deciding on its mounting technology.
1) The size and shape of the printed board.
2) Number of input and output terminals.
3) The available equipment space.
4) Desired ease of loading and unloading.
5) The type of installation accessories.
6) The required heat dissipation.
7) Required shieldability.
8) The type of circuit and its relationship with other circuits.

6. Dial-out requirements for printed boards
1) No printed board area for mounting components.
2) The influence of plugging tools on the installation distance between two printed boards.
3) The mounting holes and slots should be specially prepared in the design of the printed board.
4) When the plug-in tool is to be used in the equipment, especially its size should be considered.
5) A plug-in device is required, which is usually fixed to the printed board assembly with rivets.
6) In the mounting frame of the printed board, special designs such as load bearing flanges are required.
7) The adaptability of the plugging tools used to the size, shape and thickness of the printed board.
8) The cost involved in using plugging and unplugging tools includes both the price of the tool and the increased expenditure.
9) In order to tighten and use plug-in tools, it is required to have access to the inside of the equipment to a certain extent.

7. PCB board mechanical considerations
Substrate properties that have a significant impact on printed circuit assemblies are: water absorption, coefficient of thermal expansion, thermal properties, flexural strength, impact strength, tensile strength, shear strength and hardness. All of these properties affect both the functionality of the printed board structure and the productivity of the printed board structure. For most applications, the printed circuit board's dielectric backing is one of the following:
1) Phenolic impregnated paper.
2) Acrylic-polyester impregnated glass mats with random arrangement.
3) Epoxy impregnated paper.
4) Epoxy impregnated glass cloth.
Each substrate can be flame retardant or combustible. The above 1, 2, 3 can be punched. The commonly used material for metallized hole printed boards is epoxy-glass cloth. Its dimensional stability is suitable for high-density circuits, and it can reduce the occurrence of cracks in metallized holes. One disadvantage of epoxy-glass cloth laminates is that they are difficult to punch in the usual thickness range of printed boards, for this reason all holes are usually drilled and a copy milling operation is used to form the printed board shape.

8. PCB wire spacing
The conductors must be spaced to eliminate voltage breakdown or arcing between adjacent conductors. Spacing is variable and depends primarily on the following factors:
1) Peak voltage between adjacent wires.
2) Atmospheric pressure (working height).
3) Coating layer used.
4) Capacitive coupling parameters.
Critical impedance components or high frequency components are generally placed close together to reduce critical stage delays. Transformers and inductive components should be isolated to prevent coupling; inductive signal wires should be run orthogonally at right angles; components that generate any electrical noise due to magnetic field motion should be isolated or rigidly mounted to prevent excessive vibration.

9. PCB board wire pattern inspection
1) Whether the wire is short and straight without sacrificing function;
2) Whether the limitation of wire width is complied with;
3) Check whether the distance between wires, between wires and mounting holes, and between wires and pads must be guaranteed;
4) Whether the parallel arrangement of all wires (including component leads) is relatively close is avoided;
5) Whether acute angles (90°C or less) are avoided in the PCB board wire pattern.