PCB Tech - What should a qualified HDI PCB meet

In SMT processing, HDI PCB substrates will be inspected and tested before the processing starts, and the PCBs that meet the SMT production requirements will be selected, and the unqualified ones will be returned to the PCB supplier. For the specific requirements of the PCB, please refer to IPC-A-610C International general electronics industry assembly standards, the following are some basic requirements for PCBs of SMT manufacturers.

1. The PCB must be flat and smooth

The PCB board is generally required to be flat and smooth, and cannot be lifted up, otherwise it will cause great harm during solder paste printing and patching, such as the consequences of cracks.

2. Thermal conductivity

During reflow soldering and wave soldering, there will be a preheating zone. Usually, the PCB must be heated evenly and reach a certain temperature. The better the thermal conductivity of the PCB substrate, the less defects will be produced.

3. Heat resistance

With the development of SMT process and the requirements of environmental protection, lead-free process has also been widely used, and it has also caused the increase of soldering temperature, which puts forward higher requirements on the heat resistance of PCB. Lead-free process is used in reflow soldering. At this time, the temperature should reach 217~245 degree Celsius, and the time should last for 30~65s. Therefore, the heat resistance of general PCB should reach 260 degree Celsius and last for 10s.

Fourth, the adhesion of copper foil

The bonding strength of the copper foil should reach 1.5kg/cm2 to prevent the PCB from falling off due to external forces.

Five, bending standard

PCB has a certain bending standard, generally above 25kg/mm

Six, good conductivity

PCB as the carrier of electronic components, to realize the link between the components, it must rely on the circuit of the PCB to conduct. The PCB must not only have good conductivity, but also the circuit of the PCB cannot be directly patched up, otherwise it will The performance of the entire product will have a big impact.

Seven, can withstand solvent washing

PCB manufacturers tend to get dirty during production, and often need solvents such as washing water for cleaning. Therefore, PCBs must be able to withstand the washing of solvents without causing adverse reactions such as bubbles.

The above are some basic requirements for a qualified PCB during SMT processing. Of course, there are other requirements, which are not introduced here.

Make full use of the front space: In situations where a large number of surface mount components are used, try to make the signal line go to the top layer as much as possible, and give the bottom layer "selflessly" to the ground. This involves countless small tricks, "PCB Tips" There is a trick in "One: Switching Pins", and there are many similar spells, which will be written in the future.

Reasonably arrange the signal lines, and "give" the important areas of the board, especially the "hinterland" (which is related to the communication of the entire board ground wire), to the ground wire. As long as it is carefully designed, this can still be achieved.

Coordination of the front and the back: Sometimes on one side of the board, the ground wire is really "destroyed". At this time, try to make the wiring on both sides coordinate with each other. At the corresponding position, leave a sufficient ground to lay the ground wire, and then pass through a sufficient number of vias with a reasonable location (considering that the vias have a large resistance), and pass the signal line that will be crossed by the "bridge" The two sides of the Taiwan Strait that are forced to divide but are reluctant to part with the hope of reunification form a whole with sufficient conductivity.