The printing stage of the assembly process is vitally important. If any errors occur during this stage, it can affect the entire assembly process. To develop the optimum solder paste printing process it is essential to fully inspect every printed PCB before starting the component placement process. There are two main methods of inspecting printed PCBs which are 2D and 3D.

Mostly, the solder printing machines contain a 2D solder inspection system but the 2D inspection has its own limitations. Though it has been used for a long time now but it has a limited inspection capability of area coverage and shorts. The system falls short of checking the expected solder paste volume and shape of solder deposits. On the other hand, the 3D solder inspection system is capable of adequately checking for solder paste area coverage and shorts and measuring the shape and volume of the solder paste deposits. 

For an effective 3D solder paste inspection process, certain parameters need to be kept in mind, let’s discuss the same.

1. It is important to have data that exactly represents the stencil being used and so the expected solder paste deposits. The modified data that is used to manufacture the stencil is the data needed for the programming of solder paste inspection machines and so should be requested to make the process as easy as possible.
2. The inspection speed is an important factor when using the SPI machine for a high-speed production line. Most machines will have a specified inspection speed to ensure the machine selected is capable of keeping up with the processing time of the largest board to be processed.
3. Based on the sensor and lighting technology, the cost of the solder paste inspection machines can vary greatly. Look out for certain features and the number of projectors installed within the machine for repeatability and accuracy.
4. When processing large batch numbers it is important to consider the ability to connect the SPI machine to the printer. This enables automatic adjustment of certain parameters such as the alignment.  By doing this the two machines act as one and need less operator interaction. 
5. The graphical user interface is important to get the most from the machine selected. It enables ease of use and understanding of the information displayed.
6. Lastly, it is important to control the solder paste printing process and its effect on the complete process. If a defect is not detected during the early stages, the investment in a 3D solder paste inspection machine should be seriously considered.

With ever-increasing complexities and the components becoming smaller, controlling the solder paste printing process is becoming a tedious job. This has raised the demand for an automated inspection process. Solder paste inspection machines are a significant investment but the benefits of tightly controlling the manufacturing process will pay back in the long term by reducing rework and improving yield.