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How Much Do You Know About PCB?​


In the PCB copy board, PCB design, to the final PCB mass production, PCB assembling is also a very important thing, which not only involves the quality standard of PCB circuit board, but also affects the cost of PCB production.

Under the premise of ensuring the quality of PCB circuit board, how to make reasonable and effective board assembly, so as to save raw materials, PCB copying companies, PCB production companies pay great attention to solve a problem.

PCB assembling process requirements:

For irregular graphics, there will be a gap after the assembling board, and then the two corners of the assembling board shall not be hollowed out (at least one side is not hollowed out), otherwise the positioning hammer of the SMT machine can not be located, resulting in being unable to play the patch. Please pay attention to PCB assembling process requirements, for double panel must pay attention to the pad through hole metallization (PHT) and nonmetal (NPTH).

The main contents of PCB assembly specification and standard:

1. PCB board width ≤260mm (SIEMENS line) or ≤300mm (FUJI line); if automatic dispensing is required, PCB board width × length ≤125mm×180mm.

2. The shape of PCB assembling board should be as close to square as possible. It is recommended to use 2×2, 3×3... Makeup; but don't make it a yin-yang board.

3. The outer frame (clamping edge) of PCB assembling board shall adopt a closed-loop design to ensure that PCB assembling board will not deform after being fixed on the fixture.

4. The center distance between the small plate is controlled between 75mm and 145mm.

5. There can be no large devices or protruding devices near the connection point between the outer frame and the inner board, and between the small board and the small board, and the edge of the components and PCB board should be more than 0.5mm space to ensure the normal operation of the cutting tool.

6. In the four corners of the outer frame opening four positioning holes, aperture 4mm±0.01mm; the strength of the hole should be moderate to ensure that it will not break in the process of loading and unloading the plate; the precision of aperture and position should be high, and the hole wall should be smooth without burr.

7. Each small board in the PCB assembly board should have at least three positioning holes, 3≤ aperture ≤6mm, the edge positioning hole 1mm is not allowed to wire or patch.

8. Reference symbol used for whole PCB positioning and fine-pitch device positioning. In principle, QFP with spacing less than 0.5mm should be set in its diagonal position; the positioning reference symbols used for assembling PCB sub-boards shall be used in pairs and placed diagonally on the positioning elements.

9. When setting the reference point, usually a 1.5mm unhindered welding area is left around the point.

10. Large components should have positioning posts or positioning holes, such as I/O interface, microphone, battery interface, micro switch, headphone interface, motor, etc.

PCB board other matters needing attention: 

1.  PCB should pay attention to leaving edges and grooving when assembling board.

The edge is left to have a fixed place for later welding of plug-ins or patches, and the slot is made to split the PCB board.  The process requirement of leaving edge is generally 2-4 mm.  The components should be placed on PCB board according to the maximum width.  Slotting is PROHIBIT wiring layer or material layer, specific with PCB manufacturer to agree, processing, it is OK for the designer to mark.  PCB board is for the convenience of production, improve work efficiency, you can choose. 

2.  V-groove and slotting are a way of milling the outer shape

It is easy to separate multiple boards when making a board, so as to avoid damaging the circuit board when separating.  Decide which method to use according to the shape of the single type of board you assemble.  The V-cut needs to go in a straight line and is not suitable for four types of boards of different sizes.

Makeup requirements

1. Generally, there are no more than 4 kinds. The layer number, copper thickness and surface technology requirements of each kind of plate are the same.

2. The board is to save costs. If the production process is more complex, large batch, it is recommended to produce separately. The board also bears a rejection rate of 10%-20%.