Do you know how the reworking SMDs?

Reworking surface-mount devices (SMDs) can be done using soldering irons or non-contact rework systems. While soldering irons require significant skill and aren't always feasible, rework systems are generally preferred for their efficiency and ease of use.

Rework Process Steps:

1. Melt solder and remove component(s)
2. Remove residual solder (optional for some components)
3. Apply solder paste on PCB (via printing, dispensing, or dipping)
4. Place new component and reflow

Non-Contact Rework Methods:

1. Infrared (IR) Soldering
2. Hot Gas Soldering

Infrared Soldering

Advantages:

• Easy setup
• No need for compressed air (except for cooling)
• Fewer nozzles required for various component shapes and sizes
• Uniform heating with high-quality IR systems
• Gentle reflow process with correct profile settings
• Quick response of IR source
• Temperature control directly on the component
• Reduced oxidation and flux wear
• Documented temperature profile for each process

Disadvantages:

• Nearby components must be shielded from heat
• Surface temperature varies with the component's color (dark surfaces heat more)
• Energy loss due to convection
• No reflow atmosphere possible

Hot Gas Soldering

Advantages:

• Switch between hot air and nitrogen
• High reliability and faster processing with specific nozzles
• Reproducible soldering profiles
• Efficient heating with large heat transfer
• Even heating with high-quality nozzles
• Controlled gas temperature prevents overheating
• Rapid cooling after reflow

Disadvantages:

• Slow reaction of heat generator can distort thermal profiles
• Expensive and complex nozzles needed for precision
• Risk of blowing adjacent components and causing damage
• Local turbulence can create uneven heating
• Losses from environmental influences not compensated
• Difficult direct temperature control due to high gas velocity
• Requires an adjustment and testing phase for a suitable reflow profile

In summary, rework systems, particularly non-contact methods like infrared and hot gas soldering, are essential for efficiently correcting errors and replacing defective SMDs, each with its own set of advantages and challenges.