Reliability of a Lead-Free System: 100 Points on Lead-Free Performance and Reliability, Part 1
Tuesday, August 14, 2012 | Dr. Jennie S. Hwang, H-Technologies Group
After more than a decade of lead-free manufacturing, millions of products have been produced and put to use across many industry sectors and for people in all walks of life. What is the track record for lead-free electronics?
In a holistic view, this two-part column lays out the landscape in 100 points by taking into consideration manufacturability, reliability, and future trajectory. Each of the summary points will not be discussed or elaborated. However, inquiries about any of the points for scientific base, rationale, and further discussion are welcome.
- From a supply chain perspective, lead-free electronics primarily comprises three parts: Solder joint, PCB surface finish, and components. All three components need to be lead-free for the final product to be lead-free.
- Globally, many patents on lead-free solders have been issued, yet only a small percentage of those patents have actually worked on a commercial scale.
- Technically, the design of a “robust” lead-free solder is an intricate task.
- An intricate solder composition should not be translated to instability or lack of the required stability in application.
- Metallurgical alloying, microstructure, and micro-structural evolution under an anticipated service environment are critical to the technical base.
- For obvious scientific reasons, the greatest technical challenge comes when designing alloy compositions with a melting temperature (liquidus) less than 210°C without incorporating a high percentage of Mg, Zn Bi, In, and other low-melting elements.
- R&D work in lead-free solder commenced long before the RoHS regulatory mandate.
- Since inaction of the EU’s initiative, RoHS has gone global.
- Japan is a pioneer in practice.
- Solder alloy selection in lead-free manufacturing is critical to the quality and reliability of lead-free electronic products.
- A working solder composition is dictated by the existing SMT establishment.
- A working solder composition should be dictated by the performance need for a specific application.
- Several choices of solder joint alloys are available.
- Several choices of PCB surface finishes are available.
- Several choices of lead-free components are available, albeit with some limitations.
- The PCB assembly process must work with all components for a specific design.
- Constraints in the heat tolerance of components and the PCB bare board exist.
- The choice of solder alloy drives the reflow processing temperature required.
- The choice of solder alloy drives the wave pot temperature required.
- The alloy drives process temperature and impacts reliability on both process and material fronts.
- The main SMT operation modules (printing solder paste, pick-and-place, reflow, wave, inspection, testing, etc.) remain essentially the same as in SnPb production.
- When a problem or defect occurs, the ability to separate SMT manufacturing issues from those induced or aggravated by lead-free is a prerequisite to obtaining an effective solution.
- Production defects are often attributed to lead-free (SAC system).
- No surprises in production results occur with the SAC system judging from the fundamentals and technical anticipation.
- Production yield is in sync with the best practices in SMT manufacturing.
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