Is it possible to run Pb-Free reflow without nitrogen?

Is it possible to run Pb-Free reflow without nitrogen? We know that nitrogen will improve the solderability of our assemblies, but nitrogen does adds significant cost.

L.G.S.

Expert Panel Responses

It is certainly possible to manufacture and reflow surface mount assemblies using Pb-free soldering materials without using nitrogen. As long as we are talking about SAC alloys using Type III or Type IV powder in the paste. Advances in solder paste technology have produced materials that are Pb-free air-reflow compatible that produce no-clean residues that are clear, colorless, and pin testable. Once the powder sizes go below Type IV and/or with some exotic alloys the use of nitrogen may be required in order to produce reliable, well wetted components. Where we do see a need to implement nitrogen is in the wave soldering process. The use of nitrogen reduces the amount of dross, reduces the chance of bridging and other defects.

Dr. Brian Toleno
Application Engineering
Henkel Electronics

Dr. Brian Toleno is the Application Engineering Team leader for Henkel Technologies. He is responsible for the technical service and application engineering for Henkel's electronics assembly materials, including solder paste, underfills, PCB protection materials, and underfills.

In a one word answer YES. We have many customers operating lead free processes without Nitrogen. However we have other customers running lead free processes with Nitrogen. The Nitrogen discussion continues. There are certainly benefits to Nitrogen atmosphere in a reflow oven, however your lead free solder paste, components, board material, board finish, and other factors will determine what if any benefit Nitrogen will have for your operation. In our work we have seen a dramatic improvement on the solderability of lead free solder pastes over the last six years. The first lead free solder pastes we printed and reflowed six years ago barely moved from their printed shape and position. We have all seen the pictures of lead free solder paste that remained in its printed location after reflow soldering. They certainly reflowed but almost did not spread at all. The newer lead free solder pastes we have printed and reflowed spread much better. Still not the same spreading capability as tin lead material but much better then the older lead free solder paste products. As always, work with your materials and component suppliers to identify the correct reflow environment and reflow profile for your operation.

Joe Belmonte
Principal Consultant
ITM Consulting

Mr. Belmonte has been a process engineer and process engineering manager in the electronic manufacturing industry for over 25 years, with experience in all aspects of electronic product assembly operations. He is well-known throughout Asia and SE Asia for both his process work and teaching engagements.

It is possible, but it could also be cost effective to use nitrogen. Depending upon your resources and time, it might be valuable to run an experimental design where you look at rework/scrap rate with and without nitrogen. Depending upon the cost of your product and first pass yields, the reduction in scrap might pay for the cost of the nitrogen.

Dr. Craig D. Hillman
CEO & Managing Partner
DfR Solutions

Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

The quick answer is DEFINITELY! The Japanese have been running Lead Free without nitrogen since 1999 with great success. Virtually all Camcorders, Cameras, DVD Players, TV's, Computers, Audio Equipment, etc made in Japan are made without nitrogen and WITH Lead Free Paste. There is a great article in the May issue of Circuits Assembly Magazine that goes into some detail on this subject. And Eli Westerlaken deserves all the credit so I will just forward the link: http://circuitsassembly.com/cms/content/view/3262/95/ You will need to work with your paste vendor to find a suitable formulation but as you noted that tends to be much less expensive than running nitrogen!

Marc Peo
President
Heller Industries Inc.

Mr. Peo has been with Heller Industries for over 20 years and has been President for the past 8 years. Marc has authored several industry articles on Soldering, Flux collection, nitrogen use and Lead Free conversion.

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