|Jennie S. Hwang , Ph.D., D.Sc.|
"Lead-free Production Success Requires an Open Mind"
This editorial is a response to the numerous requests and the expressed inquisitiveness from the readers who have the charge to implement a successful lead-free production. The issue in question is why the information on the production options that have been the proven success is not properly and freely disseminated.
It has been said: "The test of a first-class mind is the ability to hold opposing views at the same time, and still retain the ability to function" (F. Scott Fitzgerald). The letter and spirit of this statement fit well with the theme of lead-free production.
In implementing a new manufacturing technology or process, it is the author's belief that the success is built on the solid technological fundamentals (1) in conjunction with the real-world manufacturing know-how. It is also the author's belief that a broad-based information flow across the global continents would benefit all, leading to a true manufacturing success. Then what is meant a "success"? "Success," in this regard, is the ability and the demonstration of a high-yield, nearly defect-free, practically economical operation to produce a reliable product, whatever the product is destined for its intended usefulness.
It is further the author's belief that an effective implementation and a sound manufacturing system stem from the understanding of broad-based information as well as the knowledge of available options and their respective merits and limitations. Yes, there are indeed options in lead-free alloys and their companion processes-thoroughly-tested and production-proven approaches.
For SMT manufacturing, the alternate approaches primarily are separated and distinguished by the process temperature (reflow and wave soldering) as well as by the process window, namely, the "same-temperature" and process window as 63Sn37Pb or a "higher-temperature" or a narrower process window (2). Within the practical constraints established, such as the generally accepted flux chemistry and the SMT infrastructure, the "same-temperature" process needs to be paired with a quaternary alloy. The viable ones include the designed compositions of SnAgCuIn, SnAgBiIn, SnAgCuBi systems. The "higher-temperature" process goes with SnAgCu and SnAgBi systems. When considering alloys containing Mg or Zn, the correlation may appear to be disrupted. Actually not, since incorporating Mg or Zn is expected to fall outside the practical constraints. These conclusions are not drawn from spotty tests, nor from force-fed data. Rather, they are the results of the systematic development and evaluation on the solid footing.
Throughout the 15-year period of lead-free development in alloy materials and the associated production processes for the last 6-year, one unequivocal consolation is that the alloy material performance is perfectly in congruence with the principles of Materials Science and Engineering (1), and that the real-world production results coincide well with the experience and knowledge that have been learned during the 25-year establishment of SMT manufacturing (2).
Among many production demonstrations, one cited below is an example as reported in the previous news releases and the more current release in the Nikkei Shinbum News, (October 9, 2004), entitled "Reasons Why Hitachi Adopting Same-Temperature Type of Lead-free Alloy." Excerpt: "...Currently Hitachi in both domestic and overseas manufacturing plants has successfully implemented lead free process .... The reason for the company to be able to fully do so is because the company has managed to develop the technology to manufacture high density PCB assemblies by using the same-temperature lead free soldering.... Hitachi has decided to use SnAgCuIn with a melting temperature of 199-204degC in communication, medical equipment and large PCB boards. Hitachi made the decision to use SnAgCuIn same-temperature alloy based on its robust process and proven reliability.... Although the industry has pointed out that In is high in price but the actual cost increase will only be 20 to 30%. Furthermore, with or without In, the price of lead free alloys will be generally higher... It is not possible to use just one type of lead-free like SnAgCu with a melting temperature of 215 - 220degC. A high-temperature process is a reliability concern .... Apart from its temperature, there are products unable to be produced with SnAgCu for the targeted reliability.... The alloy must possess the nature and characteristics of the conventional SnPb alloy as SnAgCuIn ...."
Considering all on-going debates, simply put, the true data can never be defeated; and the untrue data is self-defeating. Particularly operating in such a demanding manufacturing sector, only the most suitable and reliable product/process can eventually prevail.
The viable options should be and must be made known to the industry in full disclosure, and then the choice is everyone's, based on the production and reliability requirements. This reminds me the relentless teaching of my grandfather, a most respected intellect and philosopher in his time: " Always keep an open mind, or you would make a fool of yourself". He and his teachings have always been the inspiration and discipline that I strive for. After all, only an open mind and the broad-based knowledge can lead to a success.