PCB Fabrication

This PCBA assembly reliability design in electronic assembly processing

by:A-TECH      2020-05-18
PCBA welding used in electronic assembly processing is the hot air reflow soldering, depending on the wind convection and PCB, welding plate, lead the conduction of heat. Due to the heat capacity of bonding pad, the pin size and heating conditions are different, therefore in reflow welding welding plate, pin the same time the heated to a temperature in the heating process is also different. If the temperature difference is bigger, it may cause bad welding, such as open welding of QFP pin, rope; Electronic component of the erection, shift; The contraction of BGA solder joint fracture, etc. Similarly, we can solve some problems by changing the heat capacity. In some special product design, sometimes need to/with multiple level instrumentation hole surface connection. Due to the electronic assembly processing when the wave soldering tin pin and the contact time of the wave is the welding time is very short, often for 2 ~ 3 s, if jack heat capacity is large, the temperature of the lead can reach the requirement of the welding, formation of cold welding points. In order to avoid this kind of situation, leaves often use a technique called the hole design, to separate and ground/electric welding hole, hole big current through power. Stress sensitive components should wash cloth as far as possible away from electronic assembly processing easy bending takes place in the PCB assembly. Such as in order to eliminate the bending deformation of the sheet assembly time, should as far as possible to join the sub board with the motherboard connector cloth on the edge of the sheet, distance of screw distance not more than 10 mm. For example, in order to avoid the BGA solder joint stress fracture, should avoid the BGA layout easy bending takes place when PCB assembly. BGA bad design, on the one hand take plate is easy to cause the solder joint cracking. Electronic assembly processing PCB bending, corners of BGA solder joint stress of the large, prone to cracking or fracture. Therefore, the reinforcement of BGA corners is very effective to prevent cracking Angle welds, should use special glue to reinforce, patch glue can also be used for reinforcement. This requires components when layout room, note the reinforcement on the process documentation requirements and methods. Bottom reflow welding and selective wave soldering, reflow welding process, the top face is suitable for 'top bottom, SMD SMD / / and the layout of the THC', it is now common to a layout. It is important to note that you can according to the number of bottom instrumentation component, choose different selective wave soldering process, technology, components of the distance and place to have different requirements, can be reference to the layout of the panel components requirements.
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