RMCEMC May 2007

Download the presentation here

Location: College Hill Library, room L-107, 3645 W. 112th Ave., Westminster, CO

Time: 6:30 p.m. pizza social, 7:00 p.m. meeting starts.

Traditional flux systems used in tin-lead soldering are not designed for effective soldering of higher melting temperature alloys. The activator packages used to formulate them are formulated to activate at lower temperatures and often do not remain active at the higher melting temperatures seen with lead-free. These activators which are usually low molecular weight carboxylic acids and or acidified resins tend to breakdown, sublime, or oxidize at the higher preheat and peak temperatures, resulting in re-oxidation of the surfaces to be soldered.

These new materials from the solders to the flux systems will require careful thermal profiling to achieve reliable defect free soldering. This applies to wave soldering, reflow soldering and also lead-free rework. The thermal profile will be dependant on the activator package chosen by the chemistry supplier but also on the thermal load of the assembly.

Due to potential problems with thermal damage to components and boards and the increased potential for intermetalic growth thermal profiling is a critical part of reliable lead-free solder joints. Good thermal profiling will determine the final reliability of the assembly but also impact production output.

This presentation will describe the chemistry and alloy changes associated with lead-free soldering. It will discuss the key variables associated with material selection for wave, SMT and hand soldering processes. It will show how to select the optimal flux for the best results for higher melting alloys with slower wetting speeds and reduced spread and how-to optimization.  It will detail how to make lead-free work for you.           

It will address typical defects associated with lead-free soldering and how to select the chemistry, modify the process and the thermal profile to eliminate them. Defects such as poor wetting, de-wetting, solder voids, bridges, solder balls and tombstoning usually tend to increase when transitioning to lead-free SMT.

In wave soldering defects such as incomplete hole-fill, icicling, and bridging have a propensity to increase. In rework or hand assembly cold solder joints, poor wetting, de-wetting and component board thermal damage is are popular problems encountered.

It will detail practical advice, information ready for implementation, and experiences obtained from research and industry.

The presentation also will address the equipment changes that will be required for lead-free assembly. Other points that will be covered are as follows:

• Component requirements
• Board requirements
• Possible component and board issues to consider   
• Tin whisker and lead-free finishes
• Lead-free solders SAC and SnCu based
• Equipment and process changes
• Reliability and lead-free assembly
• Mixed alloys leaded and lead-free
• Lead-free process validation steps

Bio: Peter Biocca is Senior Market Development Engineer with Kester in Deplanes, Illinois. He is a chemist with 25 years experience in soldering technologies. He has presented around the world in matters relating to process optimization and assembly.

He has been working with lead-free for over 8 years. He has been involved in numerous consortia within this time and has assisted many companies implement lead-free successfully.  He is an active member of IPC, SMTA, and ASM. He is the author of many technical papers delivered globally. He is also a Certified SMT Process Engineer.