How to Produce a Printed Circuit Board Assembly (PCBA) II

08. Optical Inspection for Solderability (AOI, Auto Optical Inspection) Option
Not every SMT production line is equipped with an AOI machine. The main purpose of installing AOI is to inspect densely populated circuit boards that cannot undergo subsequent in-circuit electrical tests (ICT). In such cases, AOI is used as a substitute.

09. Unloading
After the boards are assembled, they are returned to magazines. These magazines are specially designed so that SMT machines can automatically pick and place the boards without affecting their quality.

10. Visual Inspection of Finished Products
Regardless of whether there is an AOI station, most SMT lines will still have a visual inspection area for assembled circuit boards. The purpose is to check for any defects after the assembly process is completed.

11. Post-Soldering Repair (Touch-up)
If certain components cannot be placed using SMT, manual soldering (touch-up) is required as a post-process repair. This step is usually arranged after the final inspection to help identify whether defects originate from SMT or later processes.
Touch-up involves using a soldering iron and solder wire. During soldering, the heated iron touches the component lead until the temperature rises enough to melt the solder wire. The molten solder is then applied, and once cooled, it solidifies to attach the component to the PCB.
It should be noted that, depending on the process requirements, some touch-up operations may be scheduled even later in the production line.

12. In-Circuit Test (ICT)
The main purpose of ICT is to check for open and short circuits on the board. It can also measure basic characteristics of most components, such as resistance, capacitance, and inductance. This ensures that components have not been damaged, misplaced, or lost due to the high-temperature reflow process.

13. Functional Test
Functional testing compensates for the limitations of ICT. While ICT only checks for open and short circuits, it does not test components like BGAs or the overall functionality of the product. Therefore, functional testers are required to evaluate all the functions of the assembled circuit board.

14. Assembly Board De-Paneling
Most circuit boards are panelized (combined into multiple-in-one formats) to improve SMT production efficiency. For example, there may be 2-in-1 or 4-in-1 boards. After assembly is complete, the boards must be cut (de-paneled) into individual pieces. Even single-board panels may require removal of excess board edges (break-aways).
There are several methods of board cutting. V-grooves (V-cuts) can be designed for use with blade-type depaneling machines (scoring), or boards can be manually snapped (not recommended). For more precise boards, router machines are used for depaneling. These are less likely to damage components and PCBs, although they require more time and cost.