Part 2: EIPC’s 2018 Winter Conference in Lyon, Review of Day 1

Estimated reading time: 12 minutes

Naisbitt gave details of a case study in which the testing procedure, known as PICT, had been optimised and used to demonstrate its advantages over established test protocols in achieving six-sigma criteria in the manufacture of electronic control units. And this could be reproduced at different manufacturing sites around the world. The PICT test was complementary to material/design element release based on SIR measurements, applying an IPC B52 approach.

Bill Birch, president of PWB Interconnect Solutions, reported the results of a three-year study within the HDP User Group Multi-lam project, to determine the reliability of multiple level microvia structures following exposure to lead-free assembly.

The Multi-lam project focused on “Type III” HDI designs, characterised by stacked microvias placed either on top of buried vias or offset to the buried vias. The terms “stack-on” and “stack-offset” were used to identify the two design variants. OEM data had shown that some stacked structures could be built reliably, but it was necessary to determine what combination of structures, materials and other parameters would result in acceptable reliability. Interconnect stress testing (IST) was carried out on a variety of stack-on and stack-offset designs, on builds with a range of finished thicknesses, materials with a range of z-axis CTE, and various BGA pitches, giving 27 possible constructions and 11 million microvias. Each of the test vehicles was pre-conditioned through 6 x 260°C reflow cycles before IST, in a design-of-experiment exercise.

The stack-on designs showed a higher incidence of failure than the stack-offset designs, and the principal failure mechanism was identified as pulling-off the cap of the buried via. The recommendation was to avoid stack-on designs.

In a related study, investigating failure modes associated with back-drilling, it had been observed that back-drilled holes failed on IST before full plated-through holes, and shallow back-drilled holes were less reliable than deep back-drilled holes. It had been shown that the failures occurred within the foil at the must-not-cut layer as a result of shear stresses within the hole when there was no knee of plated copper to balance the z-axis thermal expansion. The recommendation was to avoid shallow back-drilling unless representative testing had been carried out to qualify it on a particular design.

To the delight of those familiar with his tendency to over-run, Bill Birch was applauded for concluding his presentation within the allotted time slot!

There followed three short presentations from Alstom, which provided a company background and an insight into safety standards and quality and reliability requirements in preparation for the workshop and laboratory tour.

Jose Taborda described the electronic requirements for global railways and gave an overview of the range of products and services offered by Alstom world-wide. The company had sales of 7.3 Bn euro in 2016-17 and a current order book of 10 Bn euro. Its business strategy was to remain a customer-focused organisation with a complete range of transport solutions, creating value through innovation, based on principles of operational and environmental excellence, with diverse and entrepreneurial people. The company’s vision was to become the preferred partner for transport solutions.

Dr. Eric D’Almeida gave a summary of the constraints, standards and regulations that apply to railways. The applicable standards were EN50155 for on-board electronics, EN50125 for wayside electronics and EN5012x for safety requirements. In general, customer specifications were more stringent than railway standards. Electronics were required to operate in harsh environments, with ambient temperatures of -40°C to +85°C and board temperatures up to and exceeding 100°C, up to 95% RH with possible condensation, and saline conditions in marine environments, as well as having to withstand vibration and shock. A useful life of 20 years was required, together with the ability to withstand multiple repair operations. Key requirements were reliability and safety, and the reliability requirement fell into the high-performance category, close to that of aerospace and defence.

Thomas Boutaric continued the discussion of quality and reliability, with specific reference to printed circuit boards and assemblies. The minimum specification for PCBs was IPC-A-600 Class 2, and for assemblies IPC-A-610 Class 3, and they all required qualification for technology, materials and manufacturing processes. Various ageing tests were used by Alstom to demonstrate performance and ageing characteristics: thermal cycling, vibration and shock, salt mist, SIR, damp heat and cyclic damp heat. Many processes for PCB and PCBA manufacturing were special processes, requiring to be qualified, monitored and kept under control, whether within Alstom or at its suppliers.

After a full first-day programme of sixteen excellent presentations, delegates were grateful for the opportunity to leave their conference-room chairs and walk for a while. Dressed in white gowns and shoe covers and equipped with personal audio sets, the party was split into four groups, each with a knowledgeable Alstom guide, and shown round an impressive surface-mount assembly and test shop. Certain train-spotters in the party, hoping for a glimpse of rolling-stock in manufacture, were disappointed—the heavy engineering and vehicle-building operations are carried out elsewhere! This site was focused on the design, manufacture and test of traffic management, security and information systems for the railways.

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