Ask the Experts
January 9, 2019 - Updated
July 5, 2007 - Originally Posted

AOI or X-Ray inspection?

My Company is looking for our first automatic inspection system, should we consider AOI or X-Ray inspection?


Expert Panel Responses

Both AOI and AXI offer solutions in today's complicated assembly processes. The answer to this question is usually both as they compliment each other. However when it is not possible financially to acquire a dual solution, we have to look at the type of board being assembled and the assembly issues which the customer currently has on the board. AOI can be used very efficiently as an inspection tool post reflow with false calls down below 100 ppm and no escapes. Coupled with a repair station which enables the operator to be informed of and locate the eventual defects such as missing components, tombstones, bad polarity and bad solder joints. AOI can also be used pre-reflow as a process control tool, finding defects pre-reflow, both for components and solder paste. Using SPC tools and line management software to control the process of the pick & place and screen printers. X-Ray today is not really an in-line process due to speed and the available technology. In most cases it is used as an offline system to enable operators to look more closely at issues that are found using ICT or to verify on a sampling of boards solder joint integrity of BGA and other array devices. There is no one solution to inspection, process and quality control. It depends on the type of product being manufactured and the issues we are trying to solve.

Mark Norris
Vice President Asia
Nordson Advanced Technologies
Responsible for Nordson Advanced Technology Electronic Systems throughout Asia including China, Taiwan, Korea, Japan & SE Asia. Nordson Advanced Electronic Systems includes the world leading technology companies Asymtek Dispensing, Dage X-Ray, Dage Bond Test, March Plasma, Matrix AXI & Yestech AOI.

When considering new or used inspection equipment for you facility you must first determine your basic needs. AOI and X-Ray are two entirely different types of inspection. AOI is best used for detecting presence, correct part, polarity, skew, and various solder defects. X-Ray is typically used for inspection of wiring assemblies, semiconductor packaging, and BGA solder defects that are not visible to the naked eye. If your company places numerous BGA parts and offers BGA rework it is critical to have a decent X-Ray system to assist with this process. If you are seeing a higher number of minor defects on completed circuit boards an AOI system can save you time and money. I consider both systems a must in a modern assembly shop but if you have to choose between one or the other you will need to ask yourself a series of questions about your current process to determine the system that will add the most value today.

Andrew Joos
VP of Business Development
X-Line Asset Management
Mr. Joos is responsible for all customer-facing activities for X-line Asset Management including sales and business development. He brings 10+ years of experience selling new, high-tech capital equipment to contract manufacturers, OEMs, and equipment dealers.

No right or wrong answer to this question. You should consider both. Both X-Ray and AOI have their advantages and disadvantages. The major advantage of the X-Ray system is its ability to see voids in solder joints. The AOI systems, depending where in the process you install it and the particular AOI System you select, can monitor solder paste volume, and/or component position and component presences/absence. You should consider what defects you are most interested in finding, what is the speed of the inspection you will need to maintain your required process production rate, to determine what automated inspection technology is best for your operation. We have many customers that use AOI, X-Ray, In Circuit Test (ICT), and functional tests on their products. Each inspection technology can inspect and verify different aspects of process workmanship, component functionality, and product functionality. Use you process data to determine your most common type of defects, your most costly defects to repair, and the defects that have the most significant impact on your product reliability. This data should be used to determine what type of inspection is best for your operation. The purchase of any automated inspections system should only be done after very formal detailed inspection process planning is completed. Inspection should be considered a process just as building the product is considered a process. What tools will be most effective in discovering the identified defects, in what position of the process, in what cycle time, how often, what data must be collected, what permanent corrective action will the collected data drive, how stable is your process, etc must all be considered and determined before the purchase of any automated inspection systems.

Joe Belmonte
Principal Consultant
ITM Consulting
Mr. Belmonte has been a process engineer and process engineering manager in the electronic manufacturing industry for over 25 years, with experience in all aspects of electronic product assembly operations. He is well-known throughout Asia and SE Asia for both his process work and teaching engagements.

Depends on a number of factors, including Do you have area array devices (BGA, CSP)? Are most of your soldering problems are with area array devices? Are you low mix, high volume or high mix, low volume? Yes to the first two questions and high mix, low volume points you towards Xray. It is harder to perform optical inspection at high volumes, especially with high complexity (e.g., high-end servers). In addition, AOI can be setup in a number of locations (after screen print, after placement, etc.), while Xray is best after reflow.

Dr. Craig D. Hillman
CEO & Managing Partner
DfR Solutions
Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

Although I come from the x-ray side, and unless you are putting down BGAs or have other devices/boards where the joints are optically hidden, then my observation is that most companies choose to purchase an AOI system first. However, the two types of inspection systems should not be compared as an either/or choice. They both have a part to play in inspection as complimentary techniques. So whatever you choose, it is more than likely that the other technique will need to be acquired in the future.

Dr. David Bernard
Product Manager
Dage Precision Industries
Mr. Bernard has been the X-ray Systems Product Manager at Dage for over 5 years and have been involved in all aspects of x-ray inspection and test for printed circuit board assembly applications. Prior to this, Dr. Bernard was working with radiation measurement instrumentation.

As an AOI and AXI equipment supplier, Agilent is often asked this question. The answer is that it depends upon your goals, budget, board complexity and cost of field failures. The best solution is customer specific because of these things. Generally speaking, if your primary objective is defect prevention and process control, then focusing on AOI products like 3D solder paste inspection or pre-reflow AOI are key. If your primary goals are defect containment, then post-reflow AOI and AXI are the considerations. In many cases, some combination of pre-reflow AOI (i.e. paste and/or component pre-reflow) could be utilized for process control and AXI or post reflow AOI could be used for defect containment. Where boards tend to be extremely high volume, simple technology, and single-sided boards, customers usually start with post-reflow AOI. If boards are double-side boards with many hidden joints (area array packages, through-hole, direct attach, RF shields) and a high cost of field failures, customers usually start with AXI. In an ideal world it would be best to study all of the insertion points to identify where the return on investment for you individual needs would be the greatest. A good rule of thumb is that a complementary inspection strategy is a necessity for medium and higher complexity boards.

Stacy Kalisz Johnson
Americas Marketing Development Manager
Agilent Technologies
Ms. Johnson's entry into the electronic packaging arena was as a Package Development Engineer. Stacy recently joined the Americas Field Marketing Organization as a Marketing Development Manager for the Americas where she continues to work on AOI, AXI and also In-Circuit Test.
NOTE: Ms. Johnson is no longer working at Agilent Technologies.

Both technologies compliment each other. It is very basic, if you can not see it then you need Xray, depending in the type of parts that you are placing and products you are making you will need to choose the correct system. In an Xray system you need to consider several things. X ray will not be able to recognize differences in parts as well as rotation (polarity issues) for example. A manual Xray system will only allow you to do sampling inspection of your production and you will be able to observe different areas with no automatic inspection done. There are inline systems (with automatic inspection) at a higher price that can inspect 100 % of your production but will take a very long time to program (Not recommended for today's manufacturing needs). AOI will give you 100% visual coverage (parts, solder and lead inspection) including in some cases angled cameras to find defects in J leaded components and such but will not be able to look at hidden solders ie (BGA balls, covered pads, etc). So if after looking at your product and identifying that what you need is Xray but would like the capability of an AOI system too, then you can consider a combo system that has both technologies in one. Inline AOI-Xray machines are becoming very popular these days because they combine the easy of programming of the AOI machines with the hidden defect detection of the Xray.

Giancarlo De La Garza
Nordson YESTech
Giancarlo De La Garza has more than 7 years of expertice as a service / applications egineer in the AOI and X ray industry.

Reader Comment
The decision to purchase any inspection system shouldcome from a careful analysis of your production. Your choice must depend on anumber of parameters, which include the type of your production, volume, your goals, budget constraint and motivation. Among the first questions we ask our customers is toidentify the problems they are looking to solve and the associated costs. By going over these parameters, we can start to lay outan overall inspection strategy based on our customer's goals, budgetconstraints, and the potential cost of field defects. It is vital to focus onthe value and effectiveness of all types of inspection to maximize return oninvestment into the testing solution. In a typical scenario, AOI can be used for either pre-reflowprocess improvement or to help contain defects, while AXI is primarily used forpost-reflow defect containment. Many production sites use a combination of bothapproaches. Inspection coverage offered by AOI or AXI is also a keycomponent of your decision - complex, shielded boards and a large number ofhidden solder joints are clear indicators for an X-ray inspection system, butit may be best to combine multiple inspection approaches. After considering all the above, choose the inspection strategywhich will best complement your production schedule, budget and offer bestreturn on investment. As with all production equipment, remember that areliable support network and wellcontrolled TCO can make all the difference in your investment.
Ondrej Simecek, Taiwan

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