Do You Know How The Reworking SMDs?
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:
Melt solder and remove component(s)
Remove residual solder (optional for some components)
Apply solder paste on PCB (via printing, dispensing, or dipping)
Place new component and reflow
Non-Contact Rework Methods:
Infrared (IR) Soldering
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.
Hybrid technology
Hybrid rework systems combine medium-wave infrared radiation with hot air
Advantages:
Easy setup
The low flow velocity hot air supporting the IR radiation improves heat transfer, but cannot blow away components
Heat transfer does not depend entirely on the flow velocity of hot gas at the component/assembly surface (see hot gas)
No requirement for different nozzles for many component shapes and sizes, reducing cost and the need to change nozzles
Adjustment of the heating surface possible through various attachments if required
Heating even very large / long and exotically shaped components possible, depending on the type of top heater
Very uniform heating possible, assuming high quality hybrid heating systems
Gentle reflow process with low surface temperatures, assuming correct profile settings
No compressed air required for the heating process (some systems use compressed air for cooling)
Closed loop temperature control directly on the component possible by applied thermocouple or pyrometric measurement. This allows compensation of varying environmental influences and temperature losses. Enables use of the same temperature profile on slightly different assemblies, as the heating process adapts itself automatically. Enables (re)entry into the profile even on hot assemblies
Direct setting of target profile temperatures and gradients possible through direct control of component temperature in each individual soldering process.
No increased oxidation due to strong blowing of the solder joints with hot air, reduces flux wear or flux blowing away
Documentation of the temperature elapsed on the component for each individual rework process possible
Disadvantages
Temperature sensitive nearby components must be shielded from heat to prevent damage, which requires additional time for every board. Shield must cover also from gas flow
Convective loss of energy at the component possible
