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10.7.1 Tinning, QFN/DFN Components, Manual

 
The above video demonstrates tinning on SOIC type components. During this video demonstration, the solder pot shroud and nitrogen inerting was removed to clearly show the tinning process. For more information see 10.7.2 Tinning, QFN/ DFN Components, Robotic.
 
Outline
This procedure covers manual tinning of QFN and DFN components.

Caution
Due to the need to completely control the rates of immersion and emersion of the QFP and DFN component lands and the dwell times in and between each process step, a robotic hot solder dip is recommended for QFN and DFN component tinning. Semi-automatic or purely manual solder dipping processes may not be capable of completely controlling the rates of immersion and emersion of the QFN and DFN component lands and only provide approximate dwell dipping times in the solder bath. Greater variation in the process may cause a higher chance of damage, including latent reliability problems.

Manual dipping required for full solder finish replacement is different than manual dipping currently practiced for meeting solderability requirements because of the increased need for 100% coverage on the QFN and DFN component lands to prevent whisker growth. Certain electronic component package styles may not lend themselves to robotic hot solder dipping and may require alternative processing.

Note
For robotic thinning refer to 10.7.2 Tinning, QFN/DFN Components, Robotic.

Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.

Conformance Level - Medium
This procedure may have some variance with the physical character of the original and most likely varies with some of the functional, environmental and serviceability factors.

Acceptability References
IPC-A-610 Acceptability of Electronic Assemblies
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.5 Baking and Preheating
10.1.1 Component Tinning Basics
IPC J-STD-033 Joint Industry Standard for Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Device
J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies
J-STD-020 Moisture/Reflow Sensitivity Classification for Nonhermetic Surface Mount Devices
Manufacturer's Datasheets Requirements for case temperature maximum and Moisture Sensitivity Level (MSL)
Tools and Materials
Cleaninjg System
Cleaning System
Batch or inline cleaning system for removing fluxes and contamination.
Gloves
Gloves
Disposable, puncture-resistant gloves designed for handling mild chemicals.
Hot Plate
Hot Plate
Temperature adjustable heated plate to pre-heat components and circuit boards prior to tinning and reflow.
Microscope
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
Safety Glasses
Safety Glasses
Protect your eyes and your vision with proper safety glasses.
Solder Flux
Solder Flux   Proprietary
Used to prepare solder surfaces and to prevent formation of oxides during soldering.
Solder Pot
Solder Pot
Solder pot with static or dynamic solder wave for wire and electronic component tinning.
Hot Plate
Tweezers
Multiple sizes and tip configurations of tweezers for various small parts handling needs.
Solder Pot
Vacuum Pickup Tool
Manual or powered vacuum pickup tool for handling small parts and electrinic components.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
10.7.1 Tinning, QFN/DFN Components, Manual
QFN and DFN Components.
10.7.1 Tinning, QFN/DFN Components, Manual
Figure 1. Solder pot.
10.7.1 Tinning, QFN/DFN Components, Manual
Figure 2. Vacuum pickup tool.

10.7.1 Tinning, QFN/DFN Components, Manual
Figure 3. A variety of tweezers depending on the chip component size.
10.7.1 Tinning, QFN/DFN Components, Manual
Figure 4. Hot plate used to preheat the components to reduce thermal shock.
Procedure
  1. Ensure the QFN and DFN components to be processed meet the requirements for acceptable Moisture Sensitivity Level (MSL).

    Note
    For information on baking and moisture level control see 2.5 Baking and Preheating.
  2. Setup the Solder Pot with the proper process parameters, including solder temperature. (See Figure 1.)

    Note
    Refer to the component datasheet for guidelines regarding component peak temperatures specifications and other process parameters.
  3. Turn on the Solder Pot and allow the temperature to stabilize. Test the wave to ensure the solder is flowing smoothly if a flowing wave is used.
  4. Pick up a QFN or DFN component using a vacuum pick-up tool or mechanical tweezer. (See Figure 2 and 3.)
  5. Dip or apply flux to each lead of the QFN or DFN component.
  6. If needed, place the component on a hot plate. The heated plate will heat the QFN or DFN component to activate the flux and evaporate volatiles. Pre-heating the QFN or DFN component will also reduce the likelihood of temperature shock when placed in the liquidus solder. (See Figure 4.)
  7. Dip the lands of the QFN or DFN component into the molten solder. Follow recommended timing for immersion and emersion to properly tin the entire soldered surface areas.

    Caution
    Due to the need to completely control the rates of immersion and emersion of the QFN or DFN component lands and the dwell times in and between each process step, a robotic hot solder dip is recommended for electronic component tinning. See caution note above.
  8. If the flux used is water-soluble, run the components through a filtered hot water rinse to remove the flux residues. If the flux used is not water-soluble, use the appropriate flux remover solvent to clean the QFN or DFN components.
  9. Complete the cleaning by washing the QFN or DFN components in a cleaning system.
  10. Dry the QFN or DFN components in a general-purpose oven.
  11. Visually inspect the QFN or DFN components' appearance, cleanliness, and condition. Check the QFN or DFN component lands for acceptable solder coverage and inspect the body of the QFN or DFN component for abnormalities.
  12. Before packaging for shipping, dry the QFN and DFN components again in a general-purpose oven at a temperature, and for a time that meets the QFN and DFN components stated Moisture Sensitivity Level (MSL) requirement from the manufacturer's datasheet.
Evaluation
  1. Visual examination
  2. Tests or other inspection criteria as specified by customer drawings.
Procedure for reference only.