OCCAM results in simplicity without solder
14 April 2008
There have been excited murmurings of late about a new process that could challenge the way electronic circuits are manufactured. This solderless technique, the OCCAM process, is outlined here by Joseph Fjelstad
William of Occam, the 14th century English monk, philosopher and logician is most often associated with Occam’s Razor, a principle applied often applied by scientists as a thought “litmus test” when multiple solutions to a problem present themselves. Occam postulated that the simplest solution was most likely to provide the right answer. Occam is also credited with saying “Things should not be multiplied unnecessarily” which has been translated by others as “It is vanity to do with more that which can be done with less”. The important point here is that Occam laid down a challenge of logic that can serve well in a wide range of situations and among them is manufacturing and more specifically electronics manufacture and test.
Legacy approaches to electronics manufacture have been inextricably linked to the production of electronic assemblies by soldering components to printed circuit boards and solder has been a faithful servant of the electronics industry for the last 60 years. However, in 2006 the European Union sanctioned the use of lead in electronic solder. That single and seemingly innocent and positive act has brought significant and expensive challenges to rest on the shoulders of the electronics assembly industry. In addition, and ironically, it has also has made electronics assembly both less environmentally friendly and, it appears, also less reliable. For example, the production of lead-free electronic assemblies requires the exposure of electronic circuits and components to much higher temperatures (e.g. 30°C to 40°C greater) than is required for printed circuit assembly with traditional tin-lead solder. More over, due to the greater complexity of modern electronic assemblies with two side assembly and stacked components, such high temperature exposures might occur not just once but several times.
Unfortunately, as it is well known by test and reliably engineers, exposure of electronics to higher temperatures degrades component reliability. These negative effects are not limited to integrated circuits alone. The damaging effects of heat on optoelectronic components and certain types of discrete components such as larger electrolytic capacitors have also been registered as concerns. Moreover, the use of excess energy, not only degrades reliability and shortens integrated circuit life, it also wastes energy. There are in addition other types of concerns. For example, the increasingly extensive use of tin plating as a termination finish is reopening the door to a problem once solved, specifically the problem of tin-whiskers. With component lead pitch shrinking below 0.5mm and tin whiskers capable of growing to lengths of 10mm – 12 mm, concerns of whisker risk recurrence are justifiably elevated. Finally, it is a simple fact of life that global sourcing and supply-chain expansion has greatly increased distance between electronic product designers and their suppliers. The result is a reduction in vital resources and support for domestic technology development which could result in supply line vulnerability in troubled times.
In such an environment, the electronics industry is hard pressed to assure the reliability of the electronics they are tasked to provide. In this environment, an alternative approach to electronics assembly without solder is now being proposed that has the potential to provide a simpler pathway to RoHS compliance. The process has been dubbed the Occam Process by the developers in honor of the visionary philosopher, mentioned at the outset of this article, who extolled the virtue of simplicity. The Occam process sidesteps all of the problems created by the lead-free solder directive by eliminating solder from the assembly process.
The new process is fundamentally the reverse of standard PCB assembly, in that components are first placed and then in a later step provided with interconnections. The new approach does not subject the PCB or the components of the electronic assembly to the 250°C to 270°C temperatures required to assemble the SAC alloys, which have become de facto standards for lead-free solder assembly. There is also no concern about moisture sensitivity as components will not be exposed to soldering temperatures so baking is not required. In addition concerns about flux removal from tiny spaces beneath components and between their leads are obviated because flux is not used. Finally, because the fully tested and burned-in components are completely encapsulated, concerns of mechanical shock and thermal cycling reliability of connections are vastly diminished.
A 2001 analysis of the defect distribution performed on 1 billion solder joints found that 41% of the defects were solder opens, 20% shorts, 20% solder quality issues, 8% placement problems, 8% electrical problems and 3% other concerns. The data is not likely to have changed too much over the intervening years, however it may well be that because of the new higher temperatures of assembly required for lead-free that electrical problems might have increased due to component damage but this remains to be demonstrated. Ultimately in the present paradigm, rework and repair are considered part of the normal manufacturing regimen and are presumably factored into the overall cost of assembly.
In contrast, the Occam process is fundamentally a reverse order interconnection process. The process uses, for the most part, mature, low-risk, industry-familiar core processing technologies in a proven sequence.
A key element and artifact of the process is that the electronic components are interconnected to one another by copper plating after they are assembled into their final positions and solder is completely avoided.
The basic process steps of this process embodiment are illustrated above. An interesting side benefit of the technology is that it allows for components to be assembled in an overlapped manner which is not possible in traditional circuit manufacturing.
All the connections to the component terminations are then created by copper plating step which makes the interconnections to the exposed surfaces of the terminations arrayed across the encapsulated module’s surface. Circuit patterns can be created at this point and additional layers of insulation and circuits added as necessary until all required connections are made. The interconnections can even be redesigned as needed up to the moment they are made and no high-aspect-ratio via drilling is required. Methods similar to what has been just described have been proposed by such well known companies as GE, Intel and FreeScale for the creation of multi-chip modules and packages, all of which were designed for solder assembly to PCBs. Occam type assemblies are expected to be low in cost and readily adaptable to the integration of thermal enhancements such as internal head spreaders or even heat pipes as well as EMI shielding, embedded electrical and optical components, and more.
While some have expressed concern that Occam type solderless technologies could diminish the need for testing, the contrary is likely to be true. Processes must necessarily be highly robust to allay general quality concerns but so also must the certainty of the reliability of the constituent elements used in such assemblies and it falls to those tasked with testing to make certain that all of the electronic elements used in the assembly are operating effectively before they are committed to a point beyond which there is no clear return.
In summary, the lead-free solder mandate from the EU has sparked innovations in alternatives to solder. For example Georgia Technical University recently announced their own efforts to create solder free assembly methods and it is likely that there will be many others moving this direction in the future. William of Occam’s call to simplicity echoing from the 14th century is evidently still resonating today and the prospective benefits are clearly compelling.
Joseph Fjelstad is president of Verdant Electronics.
Contact Details and Archive...
Related Articles...
Most Viewed Articles...