Effects

Although at least partly voluntarily planned, the introduction of alloys without lead and the elimination of halogenated flame-retardants are mostly forced onto the industry from the outside. Such dramatic changes to the production processes and electronic manufacturing technology warrants a re-examination of fundamental values that motivate a company. Only once these considerations have been made can one proceed to make rational decisions about the new alloys and other necessary changes. Lead-free alloys have a direct influence on many aspects of the manufacturing process. On the one hand they directly impact all matters, which relate to quality of the product, be it in the form of reliability or in its version of process defects. On the other hand they influence an entire range of other factors such as investment into new equipment, storage provisions (for different alloys, different PWBs etc.), purchasing, or even the way PWBs are laid out or designed. Waste product or dross will have to be handled differently relating back to the company’s attitude towards the environment. There may be additional process steps that the firm has to consider: cleaning and test procedures are some of the possible additional steps. All this has an effect on the cost structure (variable or even fixed) and in the final analysis, the price of the goods manufactured. It goes without saying that the market position is of interest to the corporation.

 

Considerations

The ‘lead-free’ literature, which has increased like an avalanche during the last few years without offering too much new insight, has mainly concentrated on the different bulk properties of the new solders. It was the basic physical, mechanical and chemical characteristics such as melting point, tensile strength, electrical and thermal conductivity that the industry and their laboratories have concentrated on. All these values and parameters have been derived from small samples of these alloys. It may be worth mentioning that even on this level of investigation there does not seem to be total agreement in the different papers even on some of these basic findings.

As this is the central problem for the industry attention was also directed towards the soldered joint. Here it was mainly the wetting ability – or to put it more bluntly the unwillingness to wet when compared to tin-lead-solders – that was noticed quickly. The strong temperature dependence of wetting was a significant finding: homologous temperatures made their entrance. Investigations relating to the intermetallic compound layer are few and far between. Statements on the crystalline structure and failure mechanisms of the lead-free joints are only available for some of the ‘favored’ alloys. Even if such limited data is available it was achieved by applying standard test procedures although we do not even know whether such procedures are correct or even relevant – failure of actual assemblies and products originating from the field is not available. (‘Acceleration models and acceleration factors developed for Sn/Pb solders cannot be applied’)

Information on process defect levels (deplorably often referred to as ‘solder defects’) is not available either. Since publications about dross generation revert to such dubious means as listing it with grams/minute – something that in flow soldering operations may be seen as unusual if not tenuous – seems to indicate that certain unwelcome problems that arise with lead-free are to be swept under the carpet.

Though the number of available alloys is larger than the short list usually supplied by committees – and one may be advised to take a very close look at these lists as they may, from a scientific point of view, not only be based on scientific findings – it is, on the other hand not as long as the periodic table of chemistry may theoretically suggest. It is questionable whether alloys with four, five or even more metallic components can be manufactured in large quantity within the percentage range and tolerance required. It is furthermore doubtful that such consistency can be maintained within the process – at least when flow soldering – for any reasonably acceptable production period. And that does not even take into account the change of the alloy due to scavenging of other metals (surface finish of the PWB and components) during the creation of the solder joint. Plating and base metal alloying can substantially change the resulting alloy due to diffusion processes.

This phenomenon of diffusion can have some most interesting implications. There are several patents in effect, which not only protect certain lead-free alloys but on closer reading reveal that they also cover all and every solder joint that ends up consisting of this patented alloy. As such alloys may arise by diffusion processes even with non-patented lead-free alloys, the situation is rather tricky.

 

Decisions

This brief discussion already indicates that quite a number of imponderabilities have to be considered when allowing for this important change. Just to dwell on the last point of the previous chapter, the company has to decide whether the patents apply to their product or not. If the product is manufactured in an area that is not covered by the patent and if the product does not enter into areas where the patent is not valid, there is no concern. Whether, on the other hand, these patents (some of them are held by laboratories of universities or the US government) could be challenged on the basis of ‘prior art’ can only be judged by companies with very deep pockets, as such legal action carries a rather heavy price tag. For the rest of the companies there is the possibility of buying the alloy from a license holder as these patents has been licensed rather generously. That this will involve an extra charge that amounts to at least the cost of the license is obvious. It also carries, at least potentially, the risk of being single sourced.

This situation exemplifies clearly that the burden of making a decision should not only lie on the technical side but has to be carried also by business management. And we will see that other areas must be drawn into the decision-making process.

Only once the fundamental switches have been set can one proceed with the technical selection of the ‘best’ compound. To put it bluntly: what is important to the company? Is it the cost of the product that derives from the price of the alloy, the complexity of the process, the level of defect rate achievable, perhaps the urgent investment into new equipment, training etc.? Or is it the customer and the customer’s desire to obtain high quality product? The company has to decide. The basic question is – as so frequently – what has the higher priority: money or quality?  As a scenario one can visualize either the production with a relatively cheap zinc alloy (as e.g. practiced in some companies in Japan) or with an expensive silver-containing alloy (as frequently recommended in Europe and the USA). And we do not want to suggest that ‘cheap’ solder equates with non-reliable solder joints a priori and that ‘expensive solder’ equates with a good and reliable product.

Mind you, it is entirely possible that despite all efforts, the solution has to be an expensive one. There may be requirements of the product, its pattern of use or some of the components or PWB that leave no other way out. However, we can only arrive at this point once the basic verdict has been pronounced.

 

Homework

Although very tempting, it would be strategically incorrect to hitch onto decisions that are made by larger corporations or committees. Each product, each market and consequently each process works differently. In the past such strategies ‘to follow the leader’ have backfired badly (they are big, they have resources and they have wisdom coming out of their ears…). One example among many may suffice: Take the use of colophony-based lacquers to protect the copper surfaces of PWBs. It worked relatively well for those large corporations where the PWB is not stored for more than a couple of days. However, storing it for weeks and months causes polymerization in the resin and what was once a protective layer in time becomes a contamination and a real obstacle to soldering. So much for adopting a technology unquestioned.

We may add to this a note of caution: although large corporations sometimes appear to be very liberal with their knowledge and seemingly allow smaller companies to participate in their know-how, the reality is frequently different. One may be told which replacement alloy is used but important findings such as parameter settings and special process measures are regularly deemed proprietary and a competitive advantage and consequently kept under seal.

Internal soul-searching of the company is mandatory to carry out the process successfully. Requirements such as ’20 years of performance’ do not make much sense for a product that is obsolete within a couple of years or junked after a short period of use. Such statements do not show good business sense and would only heap on expenses that in their last analysis could potentially drive the product out of its market.

 

Proposal

In case they are not readily available within the company yet, we suggest that in a type of brainstorming session all those motivators of the corporation are identified that determine the avenue the company intends to travel during the next ‘while’. Perhaps this process should be driven a little further and more be listed than actually required at this point in time. The idea is to have as complete a register as possible. Sorting those concepts and grading or weighing them can be done in a second step.

This second step consists of an evaluation of their respective importance. We may establish a measure (e.g. a point system such as: 100 points = absolutely essential to 0 points = totally unnecessary), which will permit us to estimate the significance of each one of the goals listed. This point system then will help us during the decision process on the different possible lead-free alloys, processes, components and printed circuit boards. All those replacement solders will fall to the wayside, which do not meet all the 100-point items. And the rest of them will be ranked according to their individual compliance to the agenda.

In some articles we can read more or less between the lines that this idea of ‘guidelines’ and ‘concepts’ is not only theory. About Fujitsu Siemens Computers in Augsburg we can read: „...At Fujitsu Siemens Computers we follow a very clearly defined definition with regard to quality and equipment up-time.“ Whereas Siemens A&D CD in Amberg stresses ‚competitive advantage’ and „We wanted to establish the impact of lead-free on mass production environments quickly and looked for answers to such questions as ‚how does process performance change?’ or ‚how stable will the process perform long-term?’ and ‚where will we stand with regards to cost?’. And we do not need to explain what implicitly stands behind such statements. We also find reference being made to „Leader in environmental protection“ or „protecting the health of employees and reducing any negative impact on their well-being“. Obviously, these goals are also very high on the list in importance.

It would not be difficult to continue such a list. However, the reason why we quoted from one of the papers is to underline that such approach as outlined in this article is entirely logical and realistic and not only an academic exercise. These quotes offer us ideas that lead us to important topics of such a listing.