Thinking about an x-ray system?

Industry experience indicates that the cost of finding and repairing defects on printed circuit boards increases by 5 to 10 times at each subsequent test operation. For dense, surface-mount boards, you can reduce repair costs by using x-ray inspection to find and fix defects before in-circuit test and functional test. And if you use x-ray data to modify your manufacturing process to prevent defects, you'll realize even greater long-term savings.

Before "taking the plunge" and purchasing an x-ray inspection system, however, be sure to assess both the costs and the benefits. Here are 12 questions you should address as you examine this test-strategy alternative.

To determine whether x-ray inspection will improve your manufacturing-and-test process, you first need to determine what types of faults you are looking for and whether an x-ray system can find them. Most defects on area-array devices (such as insufficient solder, poor wetting, and missing power and ground connections) can be found only with x-ray techniques, because the devices' joints are hidden from optical inspection techniques and are inaccessible to bed-of-nails test. These "walking wounded" products often pass electrical test, but will likely fail prematurely in the field.

Clearly define the problem the system must address and the objectives you have for it. Are you trying to develop an advantage over your competitors? Improve customer satisfaction? Does a customer require x-ray inspection?

Do you hope to improve your internal processes and reduce costs? Improve the reliability of your end products and reduce warranty costs? Do you hope to prevent future failures? If so, what kind of process feedback must the system provide?

The type of business you are in and its manufacturing volume will determine what type of system you need. Are you a small, in-house prototyping shop, a huge electronics manufacturing services (EMS) provider with hundreds of products and customers, or a high-volume original equipment manufacturer (OEM) building just one product at a time? Is your production process high-volume/low-mix or low-volume/high-mix? A comparatively inexpensive manual x-ray system may serve for a low-volume shop or repair depot or for process development. If higher-volume production looms on the horizon, investing in an automated system will eliminate the need to bring two separate systems on line.

Decide when you plan to you use the x-ray system and what its role will be. Will you use x-ray in full-scale production, in prototyping, or in failure analysis? Will the system be on the production floor or in a lab? Will you need this capability long term or short term? Do you plan to use the system to eliminate defects and then transfer it to another product line or facility? Are you acquiring a system simply to evaluate the feasibility of using x-ray technology, or do you plan to implement a comprehensive quality-improvement program?

The risks associated with the use of your products dictate how thorough your inspection needs to be. Does the end product require ultra-high reliability, as with spacecraft or medical implants, or do you make calculators, cell phones, or other products where a failure will not mean life or death?

The high failure cost is obvious for a pacemaker or rocket guidance system, as is the low cost for failure of a cheap kitchen timer. Sometimes, though, failure costs remain high for subtle reasons. An electronic game assembly may seem inexpensive, but field failures can lose future sales of high-profit gaming software.

Consider the components in your boards. Do your boards contain lots of BGAs, shielded parts, pin-in-paste through-hole joints, press fit connectors, and other hidden joints? Think about how these technologies will change in your next revision, and look for a system that can be adapted as your product evolves. Although a system that just meets your current requirements may seem cost-effective, the savings evaporate quickly if the system cannot meet future needs.

Determine whether you will need an automatic system or whether manual methods will suffice. Production systems and high-mix environments demand ease-of-use. Can you install the system in your manufacturing line?

The size and complexity of your boards will affect your choice of system. Transmission x-ray systems can handle single-sided boards, and many inexpensive systems can inspect small boards. Cross-section or combination x-ray systems work better on double-sided boards.

When evaluating a specific model, consider whether it is proven or brand new. How consistent (or repeatable) are its results? Does it provide measurement data (continuous variable) or attribute data (acceptable/unacceptable)? Are there products such as repair stations or software such as CAD-conversion programs and repair software that help integrate the system into your manufacturing line? How often must you calibrate the system?

Find out whether the supplier offers the training and support you need. X-ray inspection is not as intuitive as visual inspection. Training becomes a critical component in its successful implementation. System support and maintenance may be difficult or impossible without the vendor's help. What services and support does the vendor include, and for how long?

Obvious costs include equipment purchase price and depreciation, but you must also consider costs for programming and maintenance. You will need operators to run the production line and repair people to fix the equipment when it breaks. Some systems may require a custom tool or fixture for each board type or board family.

Your implementation plan should address where and how the system will be used, the timeline for buying and installing the system, the costs of purchasing and installing a system as well as hiring and training the necessary staff, who will be responsible for developing the documentation, who will service and maintain the equipment, and who will evaluate the process and communicate its results to upper management and to customers.

Convincing upper management to purchase capital equipment requires showing that the equipment will pay for itself. Defect reduction and improved yields save money. Plus, x-ray can isolate defects that no other technology can find, which can give you a competitive advantage.

After implementing an x-ray system, you will require fewer expensive, skilled people and less equipment for troubleshooting downstream steps, and you will generate less scrap. You may significantly reduce warranty costs. Higher downstream test yields and less product rework may free up some of your factory's capacity or some of its precious floor space.

Both your customers and your management must understand the benefits of x-ray inspection. Collect data about product quality and cost savings during implementation and beyond. Remember to show savings from defects that only x-ray can find and that would otherwise have escaped to customers.

You can reach Glen Leinbach at glen_leinbach@agilent.com