Test and physical analysis capabilities cut time-to-market and improve reliability

While many semiconductor companies follow the increasing trend in adopting a fabless business model, Dialog Semiconductor has done this in a unique way. Leveraging the outsourcing model to its fullest for volume manufacturing, the company still retains a prototype test facility, including physical analysis capabilities in-house. This facilitates fast ramping to volume manufacturing at the foundry and at packaging and test sub-contractors, achieving best in class industry yields and extremely high quality and reliable products. Equally important, it allows Dialog to minimise the scope of tests required and the device test time, helping to reduce unit costs. Dialog Semiconductor maintains this test and physical laboratory at Kirchheim, near Stuttgart, Germany.

Where ASIC designs are concerned, it accelerates time-to-market. In one recent example, a consumer ASIC was taken from design concept phase to a production rate of 3 million devices per month in just 9 months. The industry average for this kind of development is around 18 months.

Dialog’s obsession with enhancing product quality comes from its heritage in the automotive industry, where any device that fails has to be analysed until the reason for the fault is established, whether this is due to external factors or a weakness in the device itself. This same thoroughness is now setting the company apart in mobile consumer markets, where reliability may not be a safety critical issue but is essential to protecting valuable brand reputations.

Mirroring packaging and test procedures

Dialog’s test facility includes:

• A 50 sq.m., Class 1000 clean room equipped for state-of-the-art wafer probe testing. This is the first test where the chips can be tested at a wafer level to see if they function. This supports the ability to reproduce the probe tests performed at the foundry, an important ability in the event of issues with early wafers from the foundry.
   
• Advanced, mixed-signal Teradyne testers, including the iFlex ™ and earlier Catalyst™ test system. These mirror the test environment at our sub-contractors. Dialog’s test set up is a fully integrated, true mixed-signal test environment. Test programs for packaged parts are first developed and optimized in-house, including local design of the load boards (upon which devices are mounted for testing). In this way, a complete and proven test environment can be delivered to the sub-contractors for every device and the same environment is maintained in Dialog’s prototype test.
   
  This is an ongoing activity throughout the product lifecycle and a reflection of the company’s commitment to continuous improvement. Fabrication processes that were adopted in 2001 are still subject to improvements in yield and device performance today.
   
  The Teradyne-based prototyping testers in Kirchheim are capable of handling advanced packaging technologies, including packages with up to 250 contacts. They combine fast throughput with accurate, reliable results. As mentioned earlier, Dialog test sub-contractors use equivalent testers, ensuring consistency throughout the test programs, wherever in the world they are carried out.
   
  Product testing is a manufacturing cost, so reducing test time and performing multi-site testing are prime goals. Dramatic improvements are experienced between early batches, with yields rising from perhaps 75% first time around to 98% or higher by the time the product is running in volume production. The test time is dramatically reduced during this process and the cycle time to create this improvement can be as short as 1 to 3 weeks – an achievement that only comes as a result of investment in in-house facilities.
   
• Substrate and packaging design are also carried out at Kirchheim, where Dialog now offers a broad range of packaging options to customers for consumer, industrial and automotive applications.
   
• For small volumes and to support our local automotive customers, who typically have a very long product life cycle, Dialog also provides a limited tape and reel capability from this laboratory.

Expertise in manufacturing software

Dialog has a dedicated team of software developers that are continuously improving and automating our manufacturing processes by creating smarter or safer interfaces between different types of equipment, including testers, probers, handlers, and operator interfaces.

State-of-the-art data processing

Dialog’s approach is to build a comprehensive and efficient manufacturing data warehouse, which allows online access to detailed information for all products shipped to our customers. Additionally, we are preserving the electrical test data integrity of each chip that has passed our quality gates. This is essential for tractability and historical product investigation purposes.

Physical laboratory proactively drives quality advances

Dialog has continued to investments in the Physical Laboratory, empowering the company the ability to enhance pro-actively the quality and reliability of its devices, and to improve manufacturing yields. Although failure analysis is an important matter here, around 80% of the activities are focused on evaluating working devices and looking for ways to continuously improve them. Helping customers to understand the likely performance of components within their operating environment, i.e. soldering onto a substrate, is another important part of the work of Dialog’s physical laboratory.

The starting point for failure analysis is device identification and examination of the history of the part.

Level 1 electrical tests are followed by non-destructive inspection, including X-ray examination and/or acoustic scans. Devices are then de-capsulated, either fully or in part, and inspected visually using optical microscopes. Where the situation requires it, inspection with a scanning electron microscope (SEM) is performed. This gives information about device surface topography, contamination and other properties, such as electrical conductivity. Sample preparation plays an important roll in failure analysis, therefore the laboratory has the ability and necessary equipment to make cross-sections of the packages and silicon chips, as well as performing chemical and mechanical die de-processing.

Advanced, small geometry bond testing includes both wire pull tests and wire-ball shear tests to determine the strength of bonds and ultimate failure mechanisms.

The Physical Laboratory is equipped with ESD and latch-up testing capabilities, which, for example, allow tests to be carried out following the Human Body Model, creating pulses between 50V and 8kV, in accordance with JEDEC standards.

Accelerated ageing can be done at various temperatures (normally 125 degrees Centigrade), having the electrical functionality verified at given time intervals. The standard ageing evaluation is 1000 hours, or some 8 weeks. This enables device performance to be extrapolated out to about 5 years of normal operation, although this can be extended to 17 years using longer test time and/or higher stress temperatures.

A unique drop test for handheld devices (e.g. mobile phones) has been developed at Dialog’s Physical Laboratory in Kirchheim. This determines the quality of solder joints that attach BGA-packaged devices to printed circuit boards. This kind of information is fed back to sub-contract manufacturers enabling them to improve their processes and it is used to assist Dialog’s customers in attaining their own quality goals. Compared to the JEDEC standard, which specifies an acceleration of 1500G, Dialog’s drop test evaluates what happens at accelerations up to 7500G. After being dropped, the package of the device under test is assessed as a measure of soldering quality.

Responsible outsourcing retains control of quality and reliability

Whilst Dialog Semiconductor has followed the industry trend in outsourcing semiconductor fabrication, device packaging and test, the company has retained a uniquely tight reign on quality and reliability through investment in its own test and Physical Laboratories. In this way, Dialog continues to push the boundaries of device performance and functional density without jeopardizing product reliability. The approach also ensures the fastest possible time-to-market for new devices, and levels of technical support for customers that most fabless chip companies can only dream of attaining.