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Science of Soldering©

Engineering Curriculum

All the Knowledge Tools That Ensure Success

Other soldering courses consist of nothing but lectures and memorization. But Science of Soldering© is genuine education. With experiments and demonstrations as well as comprehensive videos and a thorough workbook, the course explains the essential science, exposes the myths, and develops a powerful “recipe” for perfect soldering.

The course teaches by troubleshooting a multifaceted hands–on soldering process problem. In solving the problem (which involves several causes rather than a single root cause), the class learns the critical scientific forces that control all soldering from simple hand soldering to the most complex machine soldering. The class then develops quality and supplier management systems to prevent defects rather than allowing process mistakes and hoping inspection will find the defects.

And we'll roll up our sleeves to help you implement the new knowledge on the shop floor.

The following draft curriculum has been designed to meet the special needs of production, quality, design and supplier quality engineers. As with all Science of Soldering© classes, it can be modified to meet your specific needs and interests.

Part 1. The Science

1. The Core Science
  • Wetting forces
  • Chemical reactions
  • Intermetallic bonds

 

2. The Science of Soldering© Recipe
3. Clean Surfaces
  •  Definition and importance
  •  Contamination
  •  Oxides

 

4. Flux
  • Defined
  • Types and attributes
  • Acidity, ionic contamination and effects on reliability
  • The real definition of no–clean flux
  • Selecting fluxes suitable for high reliability applications

 

5. Solderability
  • Definition and importance
  • Solderability of different component and PCB surfaces
  • Implications of lead–free component finishes
  • Scientific solderability management

 

6. Solder
  • Defined
  • Alloys (leaded and lead–free)
  • Mechanical properties (ductility and tensility)
  • Lead–free solder differences and techniques

 

7. Heat
  • Why heat is needed
  • How much heat is needed
  • Failure modes from overheating
  • Scientific heat control and elimination of damage during hand soldering

 

8. Soldering vs. Welding
  • Definitions
  • Significance of surfaces that melt during “soldering” vs. surfaces that do not melt (the overlooked lead–free issue)
  • Uses of soldering and welding in electronics assembly

 

9. Troubleshooting Using the Science of Soldering© Recipe
10. Prevention of Heat Damage in Hand Soldering — The Electronics Manufacturing Sciences Solution

Part 2. Machine Soldering

1. Wave and Selective (Mini–Wave) Soldering
  • The Science of Soldering© Recipe in wave soldering
  • Physical forces determining machine setup
  • History of wave soldering evolution (and lessons for today)
  • Selecting flux
  • Selecting components
  • Role and effect of turbulent (chip) waves
  • Setting and managing wave profiles
  • Design for wave soldering
  • Techniques for maximizing process robustness
  • Mini–wave selective soldering
  • Palletized selective soldering
  • Dip selective soldering
2. Surface Mount Reflow
  • The Science of Soldering© Recipe in surface mount reflow
  • Basic concepts and history of process evolution
  • Selecting components and consumables
  • Design for reflow producibility
  • Stencils
  • Setting and managing oven profiles
  • Secrets of maximum process robustness

Part 3. Lead–Free Solders and Soldering

1. Choosing the Alloy
  • Available alloys
  • Physical properties and failure modes
  • Risks in extreme operating environments

 

2. Choosing Materials
  • Fluxes
  • Components
  • Laminates

 

3. Equipment Requirements
  • Heat
  • Ability to tolerate the alloys
  • Wave soldering machines
  • Surface mount reflow

 

4. Risk Assessment and Avoidance

 

5. Warranty Considerations

Part 4. Quality Systems and Reliability

1. Inspection and test strategies
  • Why visual criteria are not valid for reworked connections
  • Understanding the psychology of inspectors and the implications
  • 100% vs. sample inspection
  • Consequences for reliability

 

2. Reliability Criteria
  • The truth about “high reliability” soldering
  • What solder appearance reveals about machine soldering
  • What solder appearance reveals about hand soldering, repairs and rework
  • The strengths and weaknesses of A–610 and J-STD-001
  • How to identify reworked connections
  • Reliability criteria that work

 

3. Corrective Actions
  • Attacking the cause rather than the symptom
  • More inspection is not corrective action

 

4. Failures
  • Realistic product life expectancy
  • Common causes of failure and how to avoid them
  • Effects of thermal cycling on solder joint structure and reliability
  • The significance of regional failure patterns
  • Troubleshooting using the EMS Soldering Recipe and Reliability Criteria

 

Part 5. Open Discussion

Part 6. Shop Floor Implementation

The extent and length of this portion varies from project to project. The amount of Electronics Manufacturing Sciences involvement will be specified in the final quotation for services.

Science of Soldering© is the Only Course That Actually Teaches Soldering

Until recently, electronics "soldering" has actually been low-temperature welding. When surfaces melt, the process is not soldering - it is welding. Soldering is the process that works with surfaces that do not melt. Historically, most leads and other surfaces being "soldered" were plated with tin or tin/lead - and they melted when heat was applied to melt the solder. The process was easy because the melted surfaces and solder flowed together.

Not surprisingly, the electronics industry's processes were based on techniques that work well when surfaces melt. But those techniques do not work when the surfaces do not melt (i.e., during real soldering).

Because of RoHS legislation and concerns about tin whiskers, tin and tin/lead component surfaces are disappearing. And the new lead-free surfaces do not melt at soldering temperatures. This means they must be soldered rather than welded and the traditional "soldering" process doesn't work. However, training programs still teach the techniques from the days when surfaces melted (i.e., welding).

An Epidemic of Wetting Defects

The arrival of lead–free components has produced an epidemic of wetting defects that technicians disguise by using the iron to push the solder into an acceptable shape, using higher temperatures, and leaving the iron on the connection longer. (At soldering iron temperatures, solder will stick to an oxidized surface and give the false impression of reliable work.)

Lead–free parts make solderability, solderability management and flux selection critically important. As with heat control, few people have meaningful operational understanding of this essential topic.

Science of Soldering© is the only course that teaches flux selection and use, solderability and solderability management in detail.

Picking the Wrong Flux Can be Catastrophic

Successful soldering begins with picking the right flux. It's a decision that many companies get wrong, often with serious consequences.

Some of the potential consequences of poor flux selection include:

  • Corrosion
  • Dendrites
  • No fault found field failures
  • Poor wetting
  • Excessive test equipment maintenance
  • Post-soldering cleaning

Beware of Deceptive Flux Advertising

At one time, almost all electronics fluxes contained rosin. (Rosin seals the surface being soldered and prevents reoxidation of the surface after the flux acids remove the original oxides.) And there were, in essence, only two - RMA and RA. (Type R flux is impractical for production purposes.) The tests for categorizing RMA and RA fluxes were determined by the U.S. Department of Defense and Bell Laboratories.

Today, other materials are often used in place of rosin. The qualification standards have also changed. And some of the new flux formulations can cause field failures even though the new qualification system indicates that the fluxes are low risk.

The challenge of selecting the ideal flux has become  is compounded by what we consider deceptive advertising by some flux manufacturers. For example, "neutral pH" flux sold by several companies is actually highly acidic and should not be used on most electronic products.

We applied some "neutral pH" flux on a penny. The penny was quickly deoxidized (below  left). However, serious corrosion occurred in less than 3 hours (below  right).

Many "no clean" fluxes can cause corrosion and other forms of failure

Clean or "No Clean"?

Before surface mount parts arrived, quite strong (highly acidic) fluxes could be used and the residues washed off after soldering. But surface mount parts sit so close to the circuit board that flux gets trapped beneath the components and cannot be completely removed.

There are new cleaning systems that claim to be able to thoroughly remove flux residues from under all surface mount parts. Whether this is true can't be known because there is no way to measure the results. However, these systems are costly to buy and even more costly to operate. The better strategy is to use fluxes that are safe to leave on the assembly and dispense with post–soldering cleaning entirely. In other words, use a "no clean" flux.

Flux companies sell fluxes designated "no clean." But, again, there is considerable risk in taking the flux manufacturers' word. Many fluxes labeled "no clean" actually contain sufficiently strong acids that they can cause failures. They are "no clean" only in the sense that they leave behind little visible residue.

The J-STD-004 Flux Specification Problem

Where can you turn for meaningful guidance for flux selection. J-STD-004 provides some (very) rough guidelines but is inadequate?

The answer is Science of Soldering© which thoroughly explains flux selection and the related topics of solderability and solderability management.

We will help you pick the best flux for your needs. Our clients have produced millions of circuit assemblies using the no clean fluxes we helped them select. Those assemblies operate in the most extreme environments (high and low temperatures, high humidity) without failing.