THE EMS SCIENCE OF SOLDERING CURRICULUM

Soldering is the heart of electronics manufacturing. It is also the least understood process and the most common cause of product failures.

Soldering involves a small number of fairly simple chemical, physical and metallurgical forces. Unfortunately, the electronics industry has changed a rather straightforward science into an incomprehensible collection of myths and legends. The difficulty is made worse by training (telling people what to do) rather than educating (showing why)

EMS Science of Soldering© is genuine education. With experiments and demonstrations, the course explains the essential science, exposes the myths, and develops a powerful “recipe” for perfect soldering.

The course teaches by troubleshooting a complex 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 systems to prevent defects rather than allowing process mistakes and hoping inspection will find the defects.

Every class is customized to meet the special needs of the participants. Engineers (process and quality) receive in–depth education while classes for general managers are less detailed. Operator classes go to the end of the Soldering Recipe and include much more manual application practice as well as education about reliability criteria.

THE CURRICULUM

The Core Science

• Wetting forces
• Chemical reactions
• Intermetallic bonds

The EMS Science of Soldering Recipe

Clean Surfaces

• Definition and importance
• Contamination
• Oxides

Flux

• Defined
• The four uses of flux in electronics soldering
• Types and attributes
• Acidity, ionic contamination and effects on reliability
• The real definition of no–clean flux
• Selecting fluxes suitable for high reliability applications

Solderability

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

Solder

• Defined
• Alloys (includes introduction to lead–free solders)
• Mechanical properties (ductility and tensility)
• Changes in solder joints over time (normal aging, vibration and thermal stresses)

Heat

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

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

Inspection, Rework and Repair

• The vital distinction between rework and repair
• Disguising defects with touchup
• Failures caused by needless rework
• Limitations of cosmetic visual criteria for hand soldered and touched–up connections
• Overcoming operator desire to improve joint appearance

Machine Soldering

Wave and Selective (Mini–Wave) Soldering

• The EMS Science of Soldering Recipe in wave soldering
• Physical forces determining machine setup
• History of wave soldering evolution (and lessons for today)
• Selecting flux for process robustness and product reliability
• Breaking the paradigm — more preheat, lower solder temperature
• Selecting components
• Role and effect of turbulent (chip) waves
• Setting and managing wave profiles
• Design for wave soldering
• Techniques for maximizing process robustness
• Minimizing operating costs
• Mini–wave selective soldering
• Palletized selective soldering
• Dip selective soldering

Surface Mount Reflow

• The EMS 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

Equipment Selection

Maintenance Fundamentals

Lead–Free Solders and Soldering

Choosing the Alloy

• Available alloys
• Physical properties and failure modes
• Risks in extreme operating environments

Choosing Materials

• Fluxes
• Components
• Laminates

Equipment Requirements

• Heat
• Ability to tolerate the alloys
• Wave soldering machines
• Surface mount reflow

Risk Assessment and Avoidance

Warranty Considerations

Quality Systems and Reliability

• 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

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 IPC–A–610
• Reliability criteria that work
• EMS Reliability Criteria

Data Collection, Compilation and Use

• What to measure
• How to measure
• Where to measure
• When to measure
• Turning numbers into data
• Turning data into process improvements

Corrective Actions

• Attacking the cause rather than the symptom
• More inspection is not corrective action

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

Automotive Reliability (For Manufacturers of Automotive Electronics)

• Automotive requirements are different from other products
• Stresses found in automotive environments and how they affect reliability
• Consequences of unit failures
  • Safety
  • Warranty
  • Corrective action requirements
• Automotive grade vs. consumer grade components
• Design and new product validation for prevention of design–induced failures
• Layout
• Component selection (what NOT to allow in any assembly)
• Design rules for reliability
• Principles of product validation test
• Accelerated testing
• Correlation of test with real–life
• Touchup, rework and repair defined and critiqued
• Effects of each on reliability and profitability
• Proper repair procedures
• When to repair and when to scrap (setting rules for suppliers)
• Visual inspection and complications of touchup/rework

Solutions to Actual Production Problems

Samples of products causing production problems in the client’s factory are analyzed and solutions devised using the lessons of the workshop.

Open Discussion

The technical aspects of soldering are essential to success, of course. However, technical competence alone will not take the company to maximum performance. Superior communication and psychology are also essential.

Effective communication means everyone — managers, engineers and operators — use exactly the same words for exactly the same purposes. For example, "solderability" is a commonly used word in most plants but it means different things to different people; consequently, troubleshooting exercises often fail because different individuals understand the problem in different ways even though they are all using exactly the same word.

Ensuring that the terminology accurately reflects the condition is another requirement. "Cold solder" is a common example of a counterproductive term. Different people use the term to describe varying cosmetic conditions and that makes basic communication impossible. In addition, however, virtually none of the conditions described as "cold solder" are caused by lack of heat.

EMS Science of Soldering develops a common, scientifically accurate vocabulary throughout the plant. The result is more effective communication and addressing the real process issues. That doesn't happen with solder training.