EIPC 50th Anniversary Conference Day 2: The Past, the Present and the Future, Pt. 2

Estimated reading time: 11 minutes

To read the first part of this article, click here.

Well-known at EIPC conferences for her fascinating bioelectronics work, Dr. Despina Moschou, from the University of Bath in the UK, gave an update on recent developments in lab-on-PCB technology for medical diagnostic applications. She began by reviewing examples of microfluidic systems designed to bring together microscopic volumes of liquids, transducers and microelectronic components to form biosensors, and the need to identify an integration platform that could be upscaled cost-effectively to commercialise the production of cheap disposable diagnostic devices. The lab-on-PCB approach had been proposed in the 1990s, but had been sidelined by easier microfluidic fabrication processes such as soft lithography and glass/polymer processing. But it was now re-emerging as a very strong candidate, particularly because of its inherent upscaling potential. The PCB industry was well established world-wide, with standardised fabrication facilities and processes, but currently commercially exploited only for electronics. It offered opportunities for low-cost upscaling of complex micro-total-analysis systems, integrating microfluidics, sensors and electronics on the same PCB platform. There were adequate microfabrication capabilities and the integration of electronics was intuitive.

Dr. Moschou showed examples of a micro polymerase chain reaction module for DNA analysis, integrated on a PCB, and PCB biosensors for glucose and lactate. A module for measuring gamma-interferon in human serum had been developed as part of the ELISA project, and a pre-diabetes diagnosis test for mass-population preventative screening of children was in development in the CHIRP project. And biosensors for next-generation sepsis point-of-care diagnosis had been successfully ink-jet printed.

Many European academic groups were working on PCB based prototypes, the microfluidics industry was keen to engage with the PCB industry, and a substantial commercial market was forecast.

A quote from an article I wrote in PCBDesign007 made a convenient  preface to the presentation from Jan Pedersen, senior technical advisor at Elmatica in Norway:

"An enormous amount of information is needed to precisely and unambiguously define all of the fabrication details for a PCB and ensure that it is manufactured, tested, qualified and delivered exactly as the customer specified. The principal area of concern is not the image data that constitutes the board design—there are already well-established and well-accepted formats for conveying those instructions across the CAD/CAM interface—but all of the other bits and pieces of essential information needed to fulfil the order requirement that need to be communicated over the same interface. It costs the PCB industry substantial time and money interpreting this information when it is presented in different styles by different customers. A uniform language would save these costs and avoid misinterpretations."

Pedersen provided the solution with his presentation on CircuitData, an open source language for communicating PCB specification. 

Leading PCB broker Elmatica, together with its software development partner NTTY, started this initiative to improve communication of PCB Article Specifications. CircuitData was released from Elmatica as an open source site and established as a free standing organisation. The primary objectives were to reduce engineering queries to a minimum while being able to prepare quotations without exposing intellectual property.

The basic CircuitData structure divided a specification into major groups: sections, layers (including stackup information), process functions, metrics, tolerances, logistical and configuration. Pedersen discussed each of these and indicated the web addresses where further details could be found.

A CircutData material database was being compiled, that would hold material data relevant for printed circuits, and present data from different sources in one generic structure compatible with the CircuitData language. And there was a CircuitData on-line forum where new ideas could be discussed for improvements, upgrades and new technology. Also, it was planned to integrate CircuitData into Ucamco Integr8tor and IPC 2581.

“Who can join? Everyone—a language will work only when spoken!” Anyone who was interested could contribute by joining the CircuitData Forum and helping to evolve the language by discussing their requirements, adding their special parameters and encouraging colleagues, customers and suppliers to get involved.

The final conference session was concerned with new materials and processes for PCB manufacturing, moderated by Oldrich Simek, owner of Pragoboard in the Czech Republic and vice president of EIPC.

The first presentation came from Rick Nichols, Atotech’s global product manager for surface finishing, who discussed the results of a study of the initiation speed of the palladium, within an electroless nickel, electroless palladium and immersion gold (ENEPIG) system, with regard to solder joint reliability.

He commented that the reliability of solder joints became more and more important with smaller features, and the objective of the investigations was to improve solder joint reliability using high-speed shear testing as the measurement tool. Multiple designs of experiment were carried out for this optimization, and it was observed that rinsing technology had a significant impact on the results.

An Intel test vehicle was used, with 400-micron SAC 405 solder balls on 380-micron pads  assembled with customer-specified flux and reflow parameters. The assemblies were aged through one additional reflow cycle, then shear-tested at 1.8 metres per second with the shear blade set 10 microns from the surface of the PCB. 3 sets of 20 balls were tested in each run.

Initial results indicated a relationship between total shear energy and the palladium initiation stage of the ENEPIG finishing process, and this was studied further. Several methods were employed to study the palladium initiation reaction: x-ray fluorescence spectroscopy, scanning electron microscopy with energy dispersive x-ray, high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectrometry. Electrochemical methods were used to measure initiation times. There was definite correlation between palladium initiation time and shear results: the later the initiation, the poorer the result.

Bill Bowerman, director of metallisation technologies with MacDermid Enthone Electronics Solutions, presented a review of the effect of metallisation interfaces on microvia reliability. “We plate metals on surfaces and join them together!” was his opening line as he discussed the consequences of miniaturisation and multi-functionalisation of electronics: complex board architecture, mixed materials, smaller features, stacking of features, greatly reduced contact areas, lower “absolute” bond strength and a higher potential for failure under “non-optimum conditions.” He remarked that control of all aspects of the manufacturing process became increasingly critical.

Microvia reliability encompassed the ability to survive reflow assembly and the ability to survive operation through useful life. Contributing factors were the number and size of vias, their aspect ratio and shape, whether they were stacked or staggered, and their position within the stack-up. Additional factors were the cleanliness of the target pad, the type and quality of the primary metallisation, and the quality of the secondary metallisation. And it was essential to understand each process and the underlying steps of each process.

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