The precision of PCB processing involves aspects such as chip placement, welding quality, and electrical performance testing, which require strict monitoring and adjustment to meet the requirements. Absolute and relative precision control of chip placement, welding fullness, tin content, and floating height of solder beads affect welding quality. Circuit and functional testing ensure electrical performance.
1、 Accuracy requirements for patch placement
The accuracy of chip placement is crucial in PCB processing. This usually involves two aspects: absolute accuracy and relative accuracy.
Absolute accuracy: refers to the positional deviation of SMT components relative to the PCB board. Generally speaking, this deviation value needs to be controlled within a small range, usually within 0.1mm. This range is determined based on the size of the SMT components and the design requirements of the PCB board. The smaller the size of the SMT component, the higher the required absolute accuracy.
Relative accuracy: refers to the positional deviation between SMT components. This deviation value usually requires a smaller range, such as within 0.05mm. This is to ensure the mutual relationship between SMT components, especially in complex circuit boards where the relative positional relationship between SMT components is particularly important.
2、 Accuracy requirements for welding quality
In addition to the accuracy of SMT position, welding quality is also an important indicator for measuring PCB processing accuracy. This includes the soldering fullness of the components, situations of insufficient or excessive tin, and whether there are issues such as floating height or tin beads.
Welding fullness: The solder joints should be of appropriate size and shape to ensure full contact with the component pins and pads. The requirement for tin penetration is usually above 75% to ensure the firmness and conductivity of the welding.
Insufficient or excessive soldering: The amount of solder paste on the solder joint should be just right, neither too little to cause weak soldering, nor too much to cause short circuits or affect electrical performance.
Floating height and solder beads: The distance between the bottom welding surface of the component and the PCB pad should not exceed the specified value (such as 0.5mm), and excessive diameter solder beads are not allowed to appear to ensure the flatness and reliability of the welding.
3、 Accuracy requirements for electrical performance testing
In addition to the accuracy of physical position, the electrical performance testing of PCB processing is also an important aspect of measuring processing accuracy. This includes circuit testing and functional testing.
Circuit testing: By checking whether the electrical connections of each solder joint and device are correct, as well as whether the parameters such as resistance, capacitance, and inductance meet the design requirements, the electrical performance of the circuit board is ensured.
Functional testing: By simulating the actual usage environment, verify whether the PCBA can perform all functions as designed, in order to verify its overall performance and reliability.
