Careful consideration in the selection of small gage wire that is used in electronics manufacturing is critical for the quality and reliability of products. Small gage wire is typically any solid or stranded conductor that has an overall outside diameter of <0.012 inches or is <28 AWG (American Wire Gage). These conductors are used in electronics manufacturing for numerous applications. One common application for small gauge wire is for attachment to terminals such as gold cups or turret terminals. Another common use is for the soldering of discreet circuitry such as jumper wires used for rework, repair or modification of an original design. Regardless of the application, the selection of the correct gage is critical.

Improper selection of small gage wire often results in defects ranging from melted or burned insulation to laminate damage. Proper selection of small gage wire used in manual soldering operations will greatly reduce costly and time consuming changes during manufacturing and over the life of the product. Excessive and unnecessary rework and repair operations can be eliminated, thereby reducing the high cost and lost labor encountered as a result of improper design. Following some basic guidelines during the design phase will help improve the quality of the product and result in increased customer satisfaction.

Wire selection should only be made after a thorough design review that addresses the following issues:

• current handling requirements
• wire type and size
• conductor and insulation materials
• minimum electrical clearance
• stripping methods
• wrap/ attachment requirements
• cleaning materials and process
• material compatibility
• wire routing
• dielectric strength
• resistance to abrasion
• staking/ bonding
• soldering tools and equipment

The selected wire must be able to carry the required current for the circuit. The wire with the smallest diameter that can carry the required amount of current should be used. The size of terminals and plated thru holes must also be carefully selected. Terminals cannot be modified to accept a conductor, and plated thru holes must have a conductor to hole diameter ratio of 1:1.5.

The most common conductor used in wire is copper. The IPC recommends a solid, insulated copper wire with tin/lead plating. When using stranded conductors, tinning is necessary to prevent strand separation and oxidation. If flux is used for tinning, cleaning processes need to be documented.

The insulation material needs to be able to withstand the temperatures of the soldering process, cleaning methods, and the environment to which it is subjected to. The dielectric strength of the insulation should be equal to or better than that of the board insulation material. For example, polyvinyl chloride (PVC) would not be a proper selection for soldered terminations since it has a maximum insulation temperature of 105°C. PVC insulated conductors are more commonly used for mechanical attachments such as crimped connections. Teflon insulation is able to withstand temperatures between 200°C and 260°C, making it the most popular choice for soldered attachments. Resistance to abrasion, flexibility and water submersion requirements must also be considered.

The minimum electrical clearance must be maintained between any non-common conductors including uncoated traces, adjacent components and hardware (this should be stated in the assembly drawings). Requirements for minimum electrical clearances can be found in IPC-2221, Generic Standard on Printed Board Design.

When staking or bonding materials are used to secure jumper wires, the materials and methods used must be compatible with subsequent processes such as cleaning and conformal coating application. Assemblies using jumper wires for rework or modification should be uniform in routing. Wire length, direction of conductors, and staking or bonding requirements need to be documented and available to assembly technicians. Wrap and attachment requirements for jumper wires can be found in Section 11 of the IPC-A-610-C, Acceptability of Electronic Assemblies. Proven procedures for jumper wire attachments can be found in IPC7721.

Chemical, mechanical and thermal stripping methods can be used for the removal of insulation. When using a chemical stripping method, a cleaning process must be employed to remove harmful and corrosive residues.

In working with much smaller wires and conductors, the availability of special tools and equipment is usually needed. Special fixtures and holding devices may need to be designed.

In today’s industry, businesses cannot afford the cost associated with lost labor, scrap and dissatisfied customers. With a proper design review, the proper selection of high reliability, small gage wiring can easily be achieved.