7.5.3 Soldering Surface Mount Gull Wing Components, Hot Gas Method

Outline
This procedure covers the general guidelines for soldering surface mount Gull Wing components. There is basically only one type of Gull Wing component. Whether leads are on two sides or four sides, or whether the component is large or small, the soldering principles are the same.

Minimum Skill Level - Intermediate
Recommended for technicians with skills in basic soldering and component rework, but may be inexperienced in general repair/rework procedures.

Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.

Acceptability References
IPC-A-610 12.0	Surface Mount Assemblies
Procedure References
1.0	Foreword
2.1	Handling Electronic Assemblies
2.2	Cleaning
2.5	Baking And Preheating
7.1.1	Soldering Basics
7.1.2	Preparation For Soldering And Component Removal
7.1.3	Solder Joint Acceptability Criteria

Kits and Systems

Heat Shield Kit
Kit includes tools and materials needed to protect heat sensitive area of a circuit board during rework.

Soldering Skills Practice Kit
Training kit to practice circuit board soldering skills prior to testing for certification.

Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.

Additional Items and Supplies

Cleaner
General purpose cleaner for removing contamination.

Hot Air Tool
Tool and nozzles to deliver precise flow of hot air.

Microscope
Precision microscope with stand and lighting for work and inspection.

Solder Paste

Solder paste for component soldering and rework.

Wipes
Nonabrasive, low-linting wipes for cleanup.

Heat Shield
During component rework, protection of nearby components is often mandatory to avoid collateral heat damage or inadvertent reflow. Collateral heat damage or unintended reflow of adjacent component solder connections can result in component damage, oxidation, de-wetting, pad damage, wicking, starved joints, and scorching. The rework technician must constantly be aware of the effect of heat on the target device or circuit, plus how it affects components near the target device on both sides of the assembly.

235-4010 Heat Shield Blanket
These are 5" x 7" sheets of fiberglass fabric, aluminum foil laminate with a pressure-sensitive adhesive backing. Heat Shield Blanket is designed to reflect 90% of the radiant heat energy. It will withstand continuous heat in the leaded and lead-free solder melt temperature range and short-term exposure at temperatures up to 1000°F/538°C. Heat Shield Blankets can be used in conjunction with Heat Shield Plates to create a more robust thermal shield with a more rigid structure.

235-4060 Heat Shield Plates
These are light gauge 5" x 7" aluminum sheets used primarily when simple heat deflection is required. Heat Shield Plates are easy to size, cut, form, and bond or tape into place using the high-temperature mask or high-temperature tape supplied in the kit. When using Heat Shield Plate material to deflect heat, leave a small space between the Heat Shield Plate and the protected component or area to avoid direct contact transfer of heat.

115-9010 Mask, High Temperature
This product is a high-temperature, quick cure, synthetic latex, peel-able solder mask supplied in syringes with dispensing needles. This mask can create free-form heat shielding or seal the edges of the Heat Shield Blanket or Heat Shield Plates. This mask cures at room temperature in 5 minutes. Once dried, it can be peeled off after use.

Images and Figures

Surface Mount Gull Wing Component

Figure 1: Add a small bead of solder paste along the row of pads.

Figure 2: Move the tool back and forth to heat all the solder joints until complete solder melt is observed.

Procedure

Add a small bead of solder paste along the row of pads. (See Figure 1)
Place the component in position.
Adjust the pressure and temperature output of the hot air tool.
Direct the hot air over the component with the hot air tool tip approximately 2.50 cm (1.00") from the solder joint. This initial heating will pre-dry the solder paste.
Note: Solder paste has a dull flat appearance when dried.
When the solder paste has dried, move the hot air tooltip to approximately 0.50 cm (0.20") above the component. Move the tool back and forth to heat all the solder joints until complete solder melt is observed. (See Figure 2)
Remove the tool. Wait a moment for the solder to solidify.
Clean, if required, and inspect.

Solder Joint Acceptable Criteria - Gull Wing Components

Feature	Dim	Class 1	Class 2	Class 3
Maximum Lead Side Overhang	1	No more than 50% of the lead width or 0.50 mm (.020") whichever is less.	No more than 50% of the lead width or 0.50 mm (.020") whichever is less.	No more than 25% of the lead width or 0.50 mm (.020") whichever is less.
Maximum Toe Overhang	2	Does not violate minimum electrical clearance.	Not acceptable.	Not acceptable.
Minimum End Joint Width	3	50% of the lead width.	50% of the lead width.	75% of the lead width.
Minimum Side Joint Length: Lead thickness greater than 3X lead width	4	Equal to the lead width or 0.50 mm (.020") whichever is less.	3 times the formed foot length or 75% of the formed foot length, whichever is longer.	3 times the formed foot length or 75% of the formed foot length, whichever is longer.
Minimum Side Joint Length: Lead thickness less than 3X lead width	4	Equal to the lead width or 0.50 mm (.020") whichever is less.	Equal to 100% of formed foot length.	Equal to 100% of formed foot length.
Maximum Heel Fillet Height	5	No maximum, but solder must not touch the component package body.	No maximum, but solder must not touch the component package body.	No maximum, but solder must not touch the component package body.
Minimum Heel Fillet Height	6	Evidence of proper wetting.	Equal to the solder thickness plus 50% of lead thickness.	Equal to the solder thickness plus 100% of lead thickness.
Solder Thickness	7	Evidence of proper wetting.	Evidence of proper wetting.	Evidence of proper wetting.

Procedure for reference only.