SMT Solver: How to Audit OEM-EMS Assembly Capability, Part 3

In my September 2020 column I discussed the overview of an audit process to assess the manufacturing capability of OEMs or EMS companies. In my second column in this series in November I focused on technology and manufacturing capabilities of the supplier. We will conclude this three-part series with questions on quality and RoHS compliance.

Even though I have divided the questions into various areas, there are going to be overlaps because they are interconnected. As I mentioned in my previous columns, it is not important which category these questions fall into, but that they are asked. These questions are intended to help generate other questions that are relevant to your product and the manufacturing site you plan to audit—be they at an OEM or EMS site. 

Quality and RoHS Related Questions
There is a lot of interest in AOI machines these days and there is a good reason for it. AOI systems not only collect the defect data, they analyze and plot the data to help you do the root cause analysis. The problem with most AOI systems, however, is that they are wrong quite a bit. So, it is not uncommon for companies to buy multiple AOI systems and then not really use them since operators lose confidence in them. The reality is that it is not really the fault of the AOI machines but how they are used. Most AOI systems are nothing more than a few cameras that take pictures of what you are interested in, like components and joints, and compare them to an acceptable standard (image sensor technology with computer analysis of the digital images).

Most AOI systems are very good at giving you data on simple defects like wrong components, wrong orientation, wrong polarity, and insufficient paste height or paste volume. Unfortunately, most AOI systems are placed after the reflow ovens and asked to make some difficult calls like cold solder, nonwet, dewet, and insufficient joints. These are even difficult for well-trained human inspectors who would disagree with each other. It is no wonder that AOI systems are wrong quite often. 

Therefore, when trying to assess the quality approach of a company, you need to focus on whether the company’s focus is on quality assurance or quality control. There is a big difference between these two approaches. For example, quality control implies activities after product is built such as inspection, test and repair. On the other hand, quality assurance involves activities before product is built such as DFM, use of only acceptable parts (coplanarity, solderability, moisture and temperature sensitivity), and use of a documented process recipe for all the process steps (printing, placement and reflow profiles). Quality control may not add value, but quality assurance does.

When you place the AOI system before the reflow oven in the SMT line, your focus is on preventing the defects before they happen—a quality assurance approach where AOI machines provide more reliable answers. On the other hand, when you place the AOI system after the reflow oven, your focus is on quality control so that defective products don’t get shipped to the customer. I am not suggesting that you ship the products without inspection or test which are non-value-added steps but necessary and also more difficult for most AOI machines. If you plan to place AOI machines after the reflow oven, you should lower your expectations from the AOI machines. Managing your expectation is key to happiness whether you are dealing with people or machines.

With the above background in mind, when auditing a site that uses AOI machines, you could ask questions to determine whether enough thought has gone into selecting the location of the AOI machine in the SMT line, For example, why was that location of the AOI machine in the SMT line chosen—to give an idea whether the company’s focus is on quality control or quality assurance and whether the company knows the difference.

Here are some other questions related to quality worth asking during your audit:

  • Which flux are you using for touch up and rework?
  • Have you implemented no-clean board processes?
  • Do you clean the boards anyway even though the flux is no clean? Why?
  • How clean is clean and how do you measure board cleanliness?
  • Do you perform any type of accelerated stress screening? If so, what are the range, temperature ramp and length of the test? What percent of boards?
  • Do you perform any type of functional tests? What percent of boards?
  • Which debugging analysis tools do you use for troubleshooting defective boards? Do you prefer a specific set of equipment and why?

To get an idea of the overall quality focus of the company you could ask them to describe their overall Quality organization and reporting structure and question such as:

  • Is there a formal Quality Manual and Procedures?
  • Are there different manuals for tin-lead and lead-free? Are those manuals under controlled distribution?
  • What type of indicators do you use to monitor overall quality?
  • Are formal reports issued to top management on a regular basis? If so, describe the reports.

To determine if the company really is focused on quality assurance and not on quality control, you could ask them to describe their overall SPC implementation and ask which manufacturing processes are under SPC control and review their SPC procedures and sample SPC charts.

You could ask:

  • Is there formal SPC training for all levels of employees?
  • How is the data used for process control or process improvement?
  • Is remote access into the Quality Data System made available to your customers?
  • Is there formal SPC training for all levels of employees?

Also, ask them for the type and frequency of reports available from the data system.

  • It may also be worth looking into their ESD implementation procedures. For example:
  • Are sensitive areas clearly identified (i.e., any areas where ESD sensitive material is handled out of ESD protective enclosure including transferring components from one tube to another)?
  • Do all personnel and visitors wear approved ESD protective clothing and wrist straps while in the ESD-sensitive area?
  • Are all work surfaces, dissipative or conductive, grounded through a resistor per specification?
  • Are conductive or antistatic containers used to transport ESD-sensitive material from one location to another?
  • Are ESD-sensitive areas and containers periodically audited for conformance to documented ESD guidelines?

It is also useful to get some sense of how their other customers view them. For example, you could ask if they conduct customer satisfaction surveys. And ask them to provide the customer survey form if available. You could also find out if the company also conducts an independent (unbiased) customer survey and whether they have a measurement system in place to assess the customer’s perception of their performance.

  • Is there an internal measurement system within the organization which correlates to the level of customer satisfaction?
  • Do they have specific goals for achieving total customer satisfaction, both internal and external?
  • To what extent are customer satisfaction goals disseminated and understood by everyone in the organization?
  • Does management regularly review and assess all operating systems to determine if barriers to customer satisfaction exist and are appropriate action plans then implemented?
  • Is there a method in place to obtain future customer requirements?
  • Are all findings of customer dissatisfaction reported back to the proper organization for analysis and corrective action?
  • Are customer satisfaction requirements formally defined and documented, and are they based on customer input?
  • Do all support organizations understand their role in achieving total customer satisfaction? 

You could also ask what percentages of their customers provide input on their satisfaction on their own. Are their customers aware of the role of DFM (design for manufacturability) on yield and their approach in persuading their customers to follow DFM?

Equipment maintenance and calibration procedures play a key role in achieving consistent quality.

  • Are records kept for each affected piece of equipment?
  • Is the status of calibration or maintenance required clearly visible on each piece of equipment?

You could also ask whether their quality program has been surveyed and approved by other customers. If yes, by who? Are they certified as an ISO 9000 supplier? You need to keep one thing in mind about ISO certification, though. These days most companies claim to have a process recipe since most of them are now ISO certified. However, most of them do not even come close to defining what variables are important for yield. ISO certification is a good thing but very often it is more of a marketing tool and not very helpful for building products with high yield. The ISO requirement: “Say what you do and do what you say.” So most companies don’t say much but you need a detailed recipe to produce quality product.

And finally, when assessing the capability of a company to produce quality product on a consistent basis, it is important to keep in mind that having the right design, good quality incoming materials, and an in-house process document are necessary but not sufficient. Training of personnel at all levels, from senior managers to engineers, operators and purchasing agents is critical for addressing all the issues needed to improve yield.  You want to look into the training program of the company for its personnel at all levels. Remember, no one gets up in the morning and says they’re going to screw up three things today. It is management’s responsibility to provide training at all levels. Unfortunately, training is the area that gets cut when companies face hard times.

The idea behind all the questions in this column and previous two columns is to establish whether the company has done extensive process evaluation and whether they understand the importance of critical materials and process variables on product quality and reliability.

I should also note that as mentioned in the previous column, but worth repeating, is that the intent of these questions is not to dictate the process to the company but to assess their understanding and capability. You should focus mainly on the end requirements. Let the assembler worry about how best to meet those requirements. You are simply trying to establish whether they can meet your requirements.

This column originally appeared in the January 2021 issue of SMT007 Magazine.




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