Thermal Process
Bjorn Dahle
KIC - Embedded Designs Inc.

KIC
15950 Bernardo Center Dr. #E
Sand Diego, CA 92127
tel:858-673-6050
fax:858-763-0085

Does the energy use of a reflow oven increase when running lead-free production compared to leaded applications?

Unfortunately, yes. The reflow oven needs to heat up the products to a peak temperature typically 20° to 30°C above leaded applications. That takes energy. However, Flextronics in Poland recently measured this difference in energy consumption for a product when they converted it to lead-free. The lead-free process increased energy consumption by 10.6%. The research project moved into a second phase where it used process optimization software called Auto-Focus from KIC to select the ideal lead-free oven recipe. This dropped the energy consumption to 7.8%, which was close to the original leaded energy consumption. (It is also interesting to note that optimizing the oven recipe will also save energy for leaded production. The Flextronics research found a 15% reduction in energy use with the optimized leaded oven recipe compared to the standard recipe.) To view the complete report, visit www.kicthermal.com.

How many thermocouples (TCs) should I use to profile a lead-free product?
The lead-free process window is defined as the intersection between component, solder (paste) and substrate tolerances. Due to the higher solder melting temperature, this process window shrinks, leaving little room for error. The profile on any specific point on the product depends on several influences such as the component’s thermal mass, location on the board (hotter edges and corners/cooler toward the center of the board or in high-mass areas of the board) and more. Additionally, the individual components tend to have varying specifications as they relate to the time/temperature profile. Attaching only a half dozen TCs on the product for profiling tends to be inadequate in capturing the true picture of what is happening on the product, with the exception of the simplest of applications. Enough TCs must be used to make sure that the hottest and coolest parts of the product are measured, along with any critical components. This is a clear case of “more is better.”