Can I afford not to test?

24 June 2015

With the increasing complexity of electronic technology, it is essential that your manufacturing partner has an effective test strategy in place.

Product quality plays a far greater role and coupled to that is critical timing for market entry in order to maximise market share. 

Reliability of components has increased significantly in the last 20 years and often leads to the question “Why should I bother to test?” Defects not detected at an early stage carry increasingly rising costs the later they are detected in the manufacturing process. This can lead to defective products reaching end customers, rising inventory costs and expensive resolutions.

For an EMS company to deliver an effective test solution requires a number of key elements; investment in people, in equipment and detailed communications with their customers. The earlier an EMS partner can get involved in the product development, the better they can be in defining an effective test and inspection strategy.

Dynamic EMS operates an early engagement programme to ensure all due considerations and testability analysis has been carried out at an early stage, routing out potential pitfalls that may occur at a later stage. Often this entails analysis of the product complexity and make up of PCBs including component density and type. Commercial consideration is also given to the volume profile, maturity and current stage in the lifecycle of the product.  Development of a suitable test and inspection solution then dovetails into the NPI transition process.

For an EMS partner to determine an effective strategy for an end customer can take time.  However, time is a luxury and this is where the skills, knowledge and experience of the Test Engineering department within your EMS partner can really deliver value. With experience comes understanding and this can often help head-off any potential issues that may arise as a result of the manufacturing process.

There is a number of test and inspection methods available for fault detection and the utilisation of these vary both in cost and effectiveness dependent on the volume profile and technologies under test.  

Automated optical inspection (AOI) is now very accessible in terms of affordability and comes in various guises from fully automated in-line systems to bench-top systems which offer greater flexibility and are aimed at markets with low to medium volume product profiles. When an EMS company selects an AOI system or indeed a customer selects their EMS partner, consideration must be given as to whether the installed system has the capabilities to inspect the technologies on the target boards. With the decreasing size of components and reduction in PCB real estate as markets drive us towards portable products, it is important that the selected manufacturing partner can not only manufacture your PCB but also inspect it.

Prior to the advent of AOI the industry manually inspected PCBs, but studies have proven this to be less than 65% effective and thus AOI was born to provide an essential process gate capable of identifying defects reliably. Early adopters of this technology had to overcome those dreaded false call rates, but progression in HD camera imagery and improved software processing has negated this to a major extent and delivers repeatable results.

However, inspection alone leaves a big gap in the fault spectrum and here is where electrical test is efficient. Dividing electrical test into two categories; process test and functional test helps us break down the fault spectrum we wish to detect.  

For many years In-Circuit Test (ICT) has been the mainstay and fastest method of electrical process test. Testing for shorts, opens, missing, polarity, incorrect or defective parts using this bed-of-nails technique has proven to be the most effective solution for high volume manufacturers. With companies like GenRad/Teradyne and HP/Agilent pioneering the way in automated board test they took this a step further by adding features allowing you to power up the board under test and even perform a level of functional test or Boundary Scan through integrated instrumentation. Many products utilise programmable devices where the cost resides either with an external programmer to load the device or some ICT systems offer ISP (In-System Programming) which enables device programming to be carried out during the test phase in-house. However there are drawbacks to ICT.  Fixturing and programming cost in the first instance and the requirement for test point access which needs ground up design for test (DFT) included in the design parameters.  

An alternative to ICT is the Flying Probe (FP) system and perhaps the current main contender for flexible testing today, particularly in the UK where product profiles are more typically low to medium volume. Flying Probe systems vary greatly in capabilities from basic MDA (Manufacturing Defect Analysis) to inclusion of Boundary Scan either via external connections or using a special IC open sensor which is built into many Takaya systems. The major advantage of FP is the relatively low cost to the EMS customer as no fixturing is required, only a test program needs to be written. Flying Probe offers many of the same capabilities as ICT which for many customers offers peace of mind.

Last, but by no means least we need to address technologies using devices with hidden joints such as BGAs and POP. Although AOI may capture some excess and insufficients, it is impossible for them to pick up voiding which can lead to early life failure in the field.  Here is where X-Ray delivers differentiating value as the best technique for detecting structural defects in solder joints. In addition to this, X-Ray can be used for fault detection in components themselves and can also be useful on high density connectors.

Dynamic EMS operates complimentary test and inspection methodologies to ensure customers products are fully tested and verified prior to shipment. By investing in the industry leading AOI, X-Ray, Takaya Flying Probe (x2), Teradyne ICT systems and coupling this with JTAG Boundary Scan and Functional Test, they maximise test coverage and minimise the opportunity for error. This dovetails neatly into a Finished Goods service model that many customers enjoy.

Last year Dynamic EMS secured a contract in the Commercial Aviation industry based on their ability to develop and execute a test strategy. So perhaps the question at the start should be rephrased to “Can I afford not to test?” as it is simply more expensive not to test in today’s world.


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