SMT assembly mainly consists of the following steps:
- Solder Paste Printing;
- SPI (Solder Paste Inspection)(Optional);
- Chip Mounting;
- Reflow Soldering;
- AOI (Automated Optical Inspection);
- Rework (Optional).
To optimize BGA soldering in SMT process, essential measures should be made before and during soldering process. Thus, the discussion will be displayed from two aspects: before soldering and during soldering.
- PCB Board Preparation
First, proper surface finish should be picked up to be compatible with project or product requirement. There are a couple of surface finishes available and surface finish introductions and comparison should be clear in your mind. Some products call for ROHS requirement and lead-free surface finish, lead-free HASL, lead-free ENIG or lead-free OSP can be applied.
Second, PCBs should be properly stored and applied. PCBs should be packed in vacuum and container should include moisture barrier bag and moisture sensitive indicator card. The indicator card is capable of conveniently and economically inspecting whether humidity is in the control range. The color on card can be seen to tell about the humidity within the bag and the effect of desiccant. Once the humidity inside the bag exceeds or equals indicator value and the corresponding circle will become pink.
Third, PCBs should be baked and/or cleaned. Baking can be implemented on PCBs to stop moisture from leading to soldering defects. Baking can be carried out under the temperature of 110±10℃ for two hours. Also, PCB surface may be covered by dust in the process of PCB moving and storage. Therefore, it’s so important to thoroughly clean PCBs prior to assembly. In PCBCart, ultrasonic cleaner is used on assembled PCBs to guarantee them to be totally clean. As a result, board reliability can be greatly ensured.