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Lead-free: yes, but…

Series on upcoming soldering process alternatives (part I)
Lead-free: yes, but…

Lead-free soldering will be introduced anyway. After laws that would have limited the use of lead were side-lined in the US, we have to face this situation in Europe by 2004, and in Japan even earlier. Obviously, there are, besides environmental concerns, interested groupings that are expecting increased profits from the introduction of replacements. As an example, tin producers would not be displeased when alternatives will contain more tin.

Rolf Ludwig Diehm, Seho; Werner Kruppa, Multicore; Armin Rahn, rahn-tec

The present situation demands that we re-examine the basic topic and to shed light on some of the more salient aspects. By the year 2004, we will see an increase in lead-free literature. It is not only the alloy parameters that are of interest, but components, PCBs and even the equipment. On the basis of what is known so far, we can make inference. We cannot hide, though, that much more information will be required to successfully introduce lead-free soldering.
Environmental concerns
The electronics industry uses only little of the lead when compared to other industries. Of the 2,500,000 tons of lead that are mined worldwide, only about 7,405.7 tons find their way into solder joints. As approximately the same amount of recycled lead is used, the total lead in the electronics industry amounts to very little indeed (0,6%) of the total consumption. Lead in batteries and other storage media is far ahead in this dubious field (80%).
It would not be far fetched to ask whether lead in electronics is more harmful to the environment than lead of car batteries. Some experiences (for example St. Jean, Que. Canada where two city blocks were contaminated by a battery recycling site – the owner had disappeared just in time into a country that traditionally does not extradite its citizens) seem to indicate that lead in the electronics industry causes relatively little environmental harm. Accordingly, we read in a statement by the Environ Corporation that“… all uses of lead, when taken together, have only an insignificant impact on that part of the human population that is endangered the most, i.e. small children“.
As a good part of the electronic waste is recycled already, this waste does not constitute a serious environmental hazard. Lead leachate levels for landfills across the US have been tested. AWD Technologies (Pittsburgh), the company that carried out these tests, concluded that: „none of the leachate concentrations exceeded the government’s maximum allowable limits for lead‘. Furthermore, the Department of Health in the U.S. found that: „lead tends to be immobilized by the organic and clay components of soil and remains bound in the soil‘.
In the workplace, years of studies have shown no increase in the lead levels of workers. Accordingly, the EPA in the US stated: „exposure risks to the occupation-al population and the general public at large… were so low that no further action is recommended“. Good hygiene and proper treatment of PCBs, CPTs, and naturally dross, will help. A no-smoking and no-food policy must, however, be strictly adhered to minimize any exposure risk. Washing hands thoroughly with soap, something that should be normal in countries with a high standard of living, is another safety feature.
Most electronic products are delivered in housings which exclude direct contact between the user and the assembly’s solder joints. Contamination of the user’s hands is thus precluded. Even during processing, lead vapours are not generated at the normal soldering temperatures. At 250°C vapour pressure of lead is practically zero. The few products that are used by hobbyists should be labeled accordingly. However, the tinkerer knows that such goods are electrostatically sensitive and he will treat them with appropriate respect.
Political movements
We have to conclude that the political moves in Europe are bare of all logic. Several times, the pending legislation in the EU against lead has been compared to the decision of the UN to limit the production of CFCs. As the electronics industry reacted rather speedily to the intentions of the Montreal Protocol (except for some developing countries who were convinced by appropriate monetary incentives), many may expect a similar line of development for the lead-free campaign. There are, however, some distinguishing differences:
• An EU directive is no resolution from the UN. Initiatives by the UN do not convey the same partisan relevance as those entertained by some economic entity. Other countries may not see it as threatening as if it had originated in Japan or the US or the EU. The Montreal Protocol was supported by all the major industrial countries and most of them ratified the agenda quickly.
• The decrease in the ozone layer concerned and still concerns everyone. It is a very urgent affair as many scientists are of the opinion that life would not be possible without an ozone layer. In this case, immediate action was required – something that cannot be said about the lead situation.Interestingly, this time around it is notthe scientists who suggest a NO to lead in solder!
• To clean PCBs, several alternative methods had been used successfully for years. They were adopted with ease. Experiments with inert atmosphere had been carried out by GE in the seventies and by Siemens in the eighties. The trend to fluxes with low solids content and lower activity was well under way: instead of the traditional 36 to 38%, the industry had started to use 12 to 15% for SMT soldering. Solutions were in sight, however. We have to admit that even today a number of companies still have problems with cleanliness.
• Although individual solutions for lead-free soldering exist, most specialists agree that no general solution is really available. The elimination of lead will cause many problems within the electronics community. In particular, we have to expect to make a number of changes within the process, which are necessary because of the higher melting temperatures of the alternative alloys.
Situation in other countries
The proposed legislation must of necessity contain restrictions relating to imports of lead-bearing electronic products. Without such restrictions, a good part of the European electronics industry would need to relocate outside of Europe due to cost pressure. There is no doubt that the lead-free products will be more expensive to produce. The question is: how much more expensive? Are the pessimists correct who predict a sizable increase in production cost or those who only see a minor impact?
In Japan (ever since the lead-reduction legislation was introduced in the US Senate and Congress), companies and the MITI have spent large amounts of money to find lead-free solutions for soldering. Now they see the opportunity arise to realize their early efforts. As soon as the European intentions were clear, Japan’s industry lined up behind it.
Depending upon whom you listen to in the US, the reaction is mixed. A number of positive comments are intermingled with a lot of trepidations. Some government branches seem to see certain aspects of trade restrictions looming behind the European and Japanese attitudes. It has even been mentioned that appropriate legal action by the Trade Ministry may be contemplated to protest – if necessary – against such distortion of trade practices.
Maybe one could compare such a situation with the present arguments between the US and Europe are banana imports. We should though be certain that the US values the electronics industry much higher than the banana growers in South America.
Which value is sensible?
Another question which still has to be answered is: what does the legislator call lead-free? A definition of lead-free has not yet been given. Zero comma zero, a value that would certainly suit the initiators of this move and their environmental idealism, is impossible. Modern methods of analysis are good enough to detect even single lead atoms within a metal. This kind of purity, that is 0.0 %, is unattainable even with great effort Hence, we have to establish another value.
We may want to ask another question too: what does it refer to, anyway? Is it the entire assembly, or perhaps the final product? These are for example mobile telephones, cars, TV sets, etc. The automotive industry would have some economic aspects to consider. Furthermore, how about those balancing weights on the wheels? They are, even in Scandinavia, still made of lead. Will we have to go to alternatives there, too? What do we want to use there? Uranium or gold? One specialist cynically commented that if the reference will bethe final product, we could stick with lead, as all we had to do is make the housing heavier…
The frame of reference has to be clarified specifically when it comes to import, because we have a special problem since many of the components and boards are not originally from Europe. Remarks picked up during the biggest exhibition and conference of North America, do not reflect on this situation very optimistically. Nobody really assumed that all component manufacturers would be ready with lead-free products by 2004. If not, then either we can’t import those components into the EU or we have to weaken the relevant legislation. Furthermore, a mix of lead and lead-free will only ag-gravate the reuser’s and recycler’s headaches.
The reverse side of the coin is the possibility that other countries or individual firms who maintain a domineering market position may seriously challenge Europe. If a critical component is not manufactured lead-free, then European companies have two choices: either they obtain an exemption or they discontinue the manufacture of products containing such components. A further alternative would be to manufacture such parts in Europe. However, due to the large number of parts and the relevant development costs, this latter approach must be seen as unrealistic.
Alternative solders
Among all the metals that should be available for lead-free alloys, many eliminate themselves. Some must be disregarded because of their own toxicity. It would make little sense to replace the toxic lead with some other metal that may be carcinogenic. Thought must be given to the safety of the workplace as well as the environmental impact. We know that managed properly, lead can be reused. Whether this is true for all alternative metals must first be established.
Another eliminating factor is certainly the melting point of a metal. Even now using the eutectic SnPb solders, we operate at the very limit of what our present materials (laminate and CPTs) can endure. This thermal limitation restricts our choices further. In case we have to select alloys with melting points above 220°C, one would certainly have to recommend a certification process prior to production runs. A general introduction of any such solder must be judged premature at this level of information. For large companies that want to be lead-free by 2004, the critical date to start certification may have passed already. Assuming that Murphy’s law still holds true, such programs can easily be thrown off track.
We also will have to discuss whether the new solder alloy has to be eutectic or not. The possibility of mechanical interference during solidification was one of the main reasons to select Sn63Pb37.
Since soldering spells itself wetting, alternative solders must wet those surfaces properly. Lead-bearing solders will be our benchmark because we have accumulated a lot of experience with them. Each PCB and assembly not only presents one metal to the soldering operation but quite a rather variety, and we will have to check against all of them rather than only one – as frequently found in relevant literature. On the other hand we can easily imagine that some of the finishes will be discontinued to inherent problems. We may list conditions such as voids, filling of THs, penetration into small gaps and other sources of defects – as well as lead contamination of no-lead fillets.
What aboutthe physical properties?
The physical properties must meet at least those of our present lead solders. Reliability is one of the central topics in electronics and has also initiated a parallel drive towards better solders (although not necessarily lead-free). The search is on for solders that permit a higher temperature during the use of the product or higher mechanical resistance.
The thermal and electrical conductivity of SnPb-solders should be maintained or surpassed. We should remember that soldering creates electrically conductive paths and that mechanical aspects still rank only second. The designers have, however, caught on long ago that the joint and the PCB can be used to heatsink active components, and thus thermal conductivity cannot be neglected, either.
As we are discussing potential defects,the topic of repair pushes into the light, which has to be possible. Part of the issue relates to hand soldering, part of it toproduction of solder wire. In general,solders will have to be made availablein all common forms, such as bars,wire, powder/paste, preforms, coatings (e.g. HAL), and they all have to al-low reliable use. The steadily increasing number of joints that find themselves on modern assemb-lies requires that thelow production defect rates are loweredeven further. Particularly in areas suchas BGA and flip chip, the cost scissors makedefect rates above 20dpm (in some cases 5dpm) no longer acceptable.
There is some play in the price structure of electronic products, and thus we may be able to cope with some price increases for the new alloy. However, the final price of the product does not allow a major increase. That means, if some items will increase in price, the total production process must adjust itself and compensate to some extent for the one higher factor. In other words, if the paste becomes more expensive, we cannot afford further cost increases in the PCB, more expensive components, more expensive equipment, more expensive processes, etc. Should we enter into such a spiral, the final effect would be hard to evaluate.
Don’t forgetflux chemistry
If we had to develop flux chemistry systems to accommodate the new solders, we would enter into another cost squeeze. New fluxes may entail higher cost and changed process management. It is not only wetting that we are concerned about, but the question of flux enters into the minefield of residues. The first concern would therefore be the aggressiveness of the fluxes and any potential residues. Perhaps the old issue of flux-free soldering (e.g. plasma and nitrogen) is effectivelyreborn by the introduction of lead-freesolders?
Storing, testing and precise specification of the paste is a requirement. We read the viscosity data on the „old“ tins and we have a good understanding of what they mean. We developed a feel for the thixotropic properties and work with the corn size as required. By now we have learned which effect too much oxide in the paste will produce. We programmed for the melting behaviour and read the thermal profile. Is all this knowledge now going to waste? Today, every well-run operation accounts for the amount of dross generated. Its cost is weighed against the cost of preventive measures such as nitrogen coverage. How will we handle this in the future? Will the oil intermix be revived with all its main-tenance hassles? Or will it be nitrogen all the way, and will even the small user have to place a tank behind? Is buy-back of dross, so generally accepted, a thing ofthe past because recycling has become harder?
A lot has been said and written about the availability of these metals and much of it just misses reality by a hair’s breadth. What has not entered into general consciousness is the political insecurity of some critical areas. The potential danger to supplies derived from this type of political instability has not been discussed at length. Large supplies are of no use if they are not secure for delivery. Remember,tin and lead are very equally distribut-ed all over the globe. Each region hasits own resources. This is not the casefor all replacement metals. Would wehave to send a few gunboats to keep soldering going? We rather add another condition to our alternative metal’s list: securesupplies.
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EPP 169
Die Diskussion um die EU-Gesetzgebung zur Verbannung von Blei aus Elektronikprodukten schlägt hohe Wellen. Wobei derzeit immer noch Lücken bestehen, beispielsweise wie ist „bleifrei“ definiert bei mobilen Geräten mit Bleisammler zur Spannungsversorgung bzw. bei Fahrzeugen mit voluminösen Bleiakkus ? Dabei wird die Zeit allmählich knapp, insbesondere für Großunternehmen, in denen die Umstellungsprozedur lange Wege zurücklegen muß. Nachdem vom globalen Blei-Jahresverbrauch lediglich 0,5 % auf die Elektronik entfallen, stellt sich natürlich die Frage, was passiert eigentlich mit den restlichen 99,5 % ? Ironisch formuliert: wirken sich diese nicht auch toxisch aus ?
La discussion autour de la législation européenne visant à bannir le plomb des produits électroniques fait des vagues. Des lacunes continuent de persister par exemple sur la façon de définir l’absence de plomb dans le cas des appareils mobiles alimentés par des accumulateurs au plomb ou des véhicules équipés de grosses batteries au plomb. Or le temps presse, notamment pour les grandes entreprises dans lesquelles le pro-cessus de conversion est complexe. Dans la mesureoù 0,5% seulement de la consommation totale de plomb est imputable à l’électronique, on est bien sûren droit de se demander ce qu’il en est des 99,5% restants? Ou plus ironiquement, ne sont-ils pas toxiques, eux?
La discussione riguardo alla legislazione europea per l’eliminazione del piombo dai prodotti elettronici fa molto parlare. Infatti vi sono ancora molti concetti poco chiari come per esempio la definizione di „senza piombo“ nel caso di apparecchi mobili con accumulatori di piombo per l’alimentazione di tensione oppure in caso di veicoli con grandi batterie al piombo. I tempi diventano sempre più stretti soprattutto per le grandi aziende in cui il processo di trasformazione richiede molto tempo. Se si tiene conto che il consumo annuale mondiale di piombo ricade solo per lo 0,5 % sui componenti elettronici, ci si chiede naturalmente cosa succeda con il rimanente 99,5 %. Per formularlo in maniera ironica: non è nocivo anche il resto?
Lead consumption by industry
Batteries, etc.: 80.8%
Pigments/Glass: 4.8%
Ammunition: 4.7%
Sheet Lead: 1.8%
Cable coverings: 1.4%
Casting metals: 1.1%
Brass/Bronze: 0.7%
Pipes, etc.: 0.7%
Solder (excl. electr.): 0.7%
Electronic solder: 0.5%
Others: 2.8%
Source: National Centre for Manufacturing Science
A three-part series
This article, the opener of a three part series, highlights some aspects of the background material on which we will have to paint the lead-free picture. The next article (EPP Europe issue #7/8) will provide information on some of the alternative lead-free alloys and their metallurgical characteristics. A third article (EPP Europe #10) will treat possible process changes.
Aktuelle Ausgabe
Titelbild EPP Elektronik Produktion und Prüftechnik 11

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