PCB Inspection Checklist after PCB wiring layout

Inspection after PCB wiring is also necessary, so how to check the wiring in PCB design to pave the way for later design? Some designs have many different requirements, and a PCB inspection checklist can help you keep track of everything that needs to be checked.Today author from QiHe smt pick and place machine discussing about it with you .

General PCB design drawing inspection items

1) Has the circuit been analyzed? Has the circuit been divided into basic units for smooth signal?

2) Does the circuit allow short or isolated critical leads?

3) Are the places that must be shielded effectively shielded?

4) Have you made full use of the basic grid graphics?

5) Is the size of the printed circuit board the optimal size?

6) Is the selected wire width and spacing used as much as possible?

7) Has the preferred pad size and hole size been used?

8) Are the photographic plates and sketches appropriate?

9) Is there a minimum of jumper wires used? Do jumper wires go through components and accessories?

l0) Are the letters visible after assembly? Are they the correct size and type?

11) In order to prevent foaming, has the large area of copper foil been opened?

12) Is there a tool positioning hole?

PCB electrical characteristics inspection items

1) Have you analyzed the influence of wire resistance, inductance, and capacitance? Especially have you analyzed the influence of the key voltage drop phase to ground?

2) Do the spacing and shape of the wire accessories meet the insulation requirements?

3) Is the insulation resistance value controlled and specified at key points?

4) Is the polarity adequately identified?

5) Have you measured the effect of wire spacing on leakage resistance and voltage from a geometric point of view?

6) Has the medium used to change the surface coating been identified?

PCB physical characteristics inspection items

1) Are all pads and their positions suitable for final assembly?

2) Can the assembled printed circuit board meet the shock and vibration conditions?

3) What is the spacing of the specified standard components?

4) Are loosely mounted components or heavy parts secured?

5) Is the heat dissipation and cooling of the heating element correct? Or is it isolated from the printed circuit board and other heat-sensitive components?

6) Are the voltage dividers and other multi-lead components positioned correctly?

7) Are the components arranged and oriented for easy inspection?

8) Are all possible interferences eliminated on the printed circuit board and on the entire printed circuit board assembly?

9) Is the size of the positioning hole correct?

10) Are the tolerances complete and reasonable?

11) Are the physical properties of all coatings controlled and signed off?

12) Is the hole to lead diameter ratio within an acceptable range?

PCB Mechanical Design Factors

Although a printed circuit board supports components mechanically, it cannot be used as a structural member of the entire device. At the edge of the printing plate, a certain amount of support should be carried out at least every 5 inches. The factors that must be considered in the selection and design of printed circuit boards are as follows;

1) The structure of the printed circuit board – size and shape.

2) Types of mechanical accessories and plugs (seats) required.

3) Adaptability of the circuit to other circuits and environmental conditions.

4) Depending on factors such as heat and dust, consider installing the PCB vertically or horizontally.

5) Some environmental factors that require special attention, such as heat dissipation, ventilation, shock, vibration, and humidity. Dust, salt spray and radiation.

6) The degree of support.

7) Hold and fix.

8) Easy to take off.

PCB printed circuit board installation requirements

It should be supported at least within 1 inch of all three edges of the printed circuit board. According to practical experience, the spacing between the supporting points of printed circuit boards with a thickness of 0.031–0.062 inches should be at least 4 inches; for printed circuit boards with a thickness greater than 0.093 inches, the spacing of supporting points should be at least 5 inches. Taking this measure can increase the rigidity of the printed circuit board and destroy possible resonance of the printed circuit board.

A certain type of printed circuit board usually needs to consider the following factors before deciding on the mounting technology they use.

1) The size and shape of the printed circuit board.

2) The number of input and output terminals.

3) Available equipment space.

4) Desired ease of loading and unloading.

5) Type of mounting accessories.

6) Required heat dissipation.

7) Shieldability required.

8) The type of circuit and the relationship with other circuits.

Dial-out requirements for printed circuit boards

1) Printed circuit board area that does not require mounting components.

2) The influence of plugging tools on the installation distance between two printed circuit boards.

3) Specially prepare mounting holes and slots in the printed circuit board design.

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 permanently fixed to the printed circuit board assembly with rivets.

6) In the mounting frame of the printed circuit board, a special design such as a load bearing flange is required.

7) The adaptability of the plugging tool used to the size, shape and thickness of the printed circuit board.

8) The cost involved in using the plug-in tool includes both the price of the tool and the increased expenditure.

9) In order to fasten and use plugging tools, it is required to have access to the interior of the equipment to a certain extent.

PCB Mechanical Considerations

The substrate properties that have a significant impact on printed circuit assemblies are: water absorption, coefficient of thermal expansion, heat resistance, flexural strength, impact strength, tensile strength, shear strength, and hardness.

All of these characteristics affect both the functionality of the printed circuit board structure and the productivity of the printed circuit board structure.

For most applications, the dielectric substrate for printed wiring boards is one of the following substrates:

1) Phenolic impregnated paper.

2) Acrylic-polyester impregnated randomly arranged glass mat.

3) Epoxy impregnated paper.

4) Epoxy impregnated glass cloth.

Each substrate can be flame retardant or combustible. Above-mentioned 1,2,3 can be punched. The most commonly used material for metallized hole printed circuit boards is epoxy-glass cloth, its dimensional stability is suitable for high-density circuit use, and it can minimize 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 for printed circuit boards. For this reason, all holes are usually drilled and profile milled to form the shape of the printed circuit board.

PCB Electrical Considerations

In DC or low-frequency AC applications, the most important electrical properties of insulating substrates are: insulation resistance, electrical isolation resistance, printed wire resistance, and breakdown strength.

In high frequency and microwave occasions, it is: dielectric constant, capacitance, and dissipation factors.

In all applications, however, the current carrying capacity of the printed conductors is important.

Read more: PCB Inspection Checklist after PCB wiring layout

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