Circuits Assembly Online Magazine - Adding Rework to the Test and Inspection Suite

The two processes don’t talk to each other. They should.

Not long ago, I was on a tour at a small contract manufacturer’s site that prides itself on quality. This EMS builds medical and aerospace products, among other things. In speaking about its quality plans and how it defines quality, there was a thorough review of the test and inspection plans that includes manual visual inspection (MVI), automated optical inspection, automated x-ray inspection, in-circuit test and rework. (We did not explore functional test.) Seeing the rework step included in its overall quality plan and part of the test and inspection discussion, I realized this is a very logical inclusion; one I previously had not entertained. I have written and read many papers mentioning rework and how by using AOI, AXI and ICT, a board assembler can reduce rework, impact rework costs, and so on. However, I had never educated myself on rework from the perspective that it could be included in the test and inspection suite.

Fig. 1

I decided to invest some time in learning more about rework. I understood the standard definition of rework, which is the process of removing a faulty component from a PCB and then soldering a new component. I also would categorize the process steps associated with rework to include finding a failed component, removing it, residual solder removal and soldering a replacement component with appropriate reflow. However, when I envision a rework station in a production environment, I think of a workstation with an operator using a software interface from an upstream process (i.e., AOI, AXI, ICT) to determine where a fault is and take repair action. My idealistic view shows the inspection steps from the first-pass production communicating with the rework station in a tidy, closed-loop setup. After some investigation, I have determined this is not as likely as I thought.

I have some familiarity with hand-soldering and manual rework, and while it was not in a manufacturing environment, I feel I have a good understanding of that process. In reading about rework, I confirmed time and temperature are critical to the reflow profile associated with removing and replacing components. These factors can impact long-term product quality. Hand soldering seemed risky, as I envisioned critical parts (medical, military) being reworked. Therefore, as part of my research, I visited an advanced rework equipment facility and operated one of its semiautomated rework systems (Figure 1). I was surprised at how intuitive and easy it was to use. Because I primarily deal with “automated” systems in the automated inspection world, my first thought was, Why not completely automate this process? I quickly realized, if fully automated rework is needed, that would indicate a serious manufacturing or design problem to be revisited. The ability to properly heat/cool the board/components in a reliable fashion, and accurately place the component, are the most critical factors to consider. The semiautomated system I saw could reduce and eliminate variables associated with time and temperature, thus creating a reliable reworked product.

Continuous improvement at rework appears a little different than I would have thought. While a barcode scanner may be used to call up defects, it is often manual paper systems or Excel spreadsheets that initiate rework station actions. My idealistic view of a closed-loop software connection and shop-floor systems is reserved for but a few high-volume production sites. That said, some rework operators and engineers do revisit their rework data to identify a Pareto of consistently reworked defects, and therefore attempt to solve the up-the-line problems.

It is through this effort that I have come to agree with a quote I found: “The rework and repair of printed circuit boards has never been more critical to the success of contract electronics manufacturers and OEMs than it is now.”1 Rework is a necessity. Process improvement, test and inspection will continue to improve yields and quality, but we will never achieve 100% yields. Therefore, it is critical to ensure all the right rework processes and equipment are in place to dictate long-term success. There is a great opportunity that lies ahead for inspection and test companies to incorporate rework into the test and inspection suite. As automation intensifies with AOI, AXI and ICT, and software systems that talk to one another to close the loop become available, including the rework process should be a priority.

Au.: Thank you to Robert Avila and Adrienne Gerard of Finetech for hosting my visit and for direction and consult during the preparation of this column.