7.3.2 Soldering Surface Mount Chip Components, Hot Gas Method Method

Outline
This procedure covers the general guidelines for soldering surface mount chip components. The following surface mount chip components are covered by this procedure. While all of these components are different, the techniques for soldering are relatively similar

Chip Resistors: The component body of chip resistors is made out of alumna; an extremely hard, white-colored material. The resistive material is normally located on the top. Chip resistors are usually mounted with the resistive element facing upwards to help dissipate heat.

Ceramic Capacitors These components are constructed from several layers of ceramic with internal metalized layers. Because metal heats up much faster than ceramic, ceramic capacitors need to be heated slowly to avoid internal separations between the ceramic and the metal layers. Internal damage will not generally be visible since any cracks will be inside the ceramic body of the component.

Note: Avoid rapid heating of ceramic chip capacitors during soldering operations.

Plastic Body: Another style of chip component has a molded plastic body that protects the internal circuitry. There are a number of different types of components that share this type of exterior package. The termination styles for plastic chip component packages vary considerably.

MELF: MELF - Metal Electrode Face cylindrical components. These may be capacitors, resistors, and diodes. It can be hard to tell them apart - since there is no universal coloring or component designators printed on the component bodies.

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 - 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 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
IPC7711 5.3.1	Solder Paste Method

Kits and Systems

Flex-Rack PCB Holder
Sturdy holder supports PCBs for rework, drilling, pad repair, and positioning.

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.

Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.

Wipes
Nonabrasive, low-linting wipes for cleanup.

Images and Figures

Surface Mount Chip Component

Figure 1: Add a small bead of solder paste to each pad.

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

Chip Capacitors generally have solid color bodies.

A - Stripe

Procedure

Add a small bead of solder paste to each pad. (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: When the solder paste has been pre-dried, the paste will have a dull, flat appearance.
When the solder paste has dried, move the hot air tool tip to approximately 0.50 cm (0.20") above the component. Move the tool back and forth to heat both 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 - Chip Components

Feature	Dim	Class 1	Class 2	Class 3
Maximum Component Side Overhang	1	Less than 50% of the component termination width or 50% of the pad width whichever is less.	Less than 50% of the component termination width or 50% of the pad width whichever is less.	Less than 25% of the component termination width or 25% of the pad width whichever is less.
Maximum Component End Overhang	2	Not permitted.	Not permitted.	Not permitted.
Minimum End Joint Width	3	50% of the component termination width or 50% of the pad width, whichever is less.	50% of the component termination width or 50% of the pad width, whichever is less.	75% of the component termination width or 75% of the pad width, whichever is less.
Minimum Side Joint Length	4	Evidence of proper wetting.	Evidence of proper wetting.	Evidence of proper wetting.
Maximum Fillet Height	5	Solder may overhang the pad but must not touch the non-soldered portion of the component package body.	Solder may overhang the pad but must not touch the non-soldered portion of the component package body.	Solder may overhang the pad but must not touch the non-soldered portion of the component package body.
Minimum Fillet Height	6	Evidence of proper wetting.	Evidence of proper wetting.	Equal to the solder thickness plus 25%, or equal to the solder thickness plus 0.50 mm (.020"), whichever is less.
Minimum Solder Thickness	7	Evidence of proper wetting.	Evidence of proper wetting.	Evidence of proper wetting.
Minimum End Overlap	8	Evidence of any overlap is required.	Evidence of any overlap is required.	Minimum 25% of the termination length.

Procedure for reference only.