What Is a Bobbin?

A bobbin is a circular or polygonal cylinder made by winding an electric wire to make a coil. It is mainly made from electrically insulating resin, but since terminals are generally made from metal, the high cost of using both resin and metal parts are an issue. Therefore, resin terminal bobbins that are integrally molded with resin are currently under development.

Figure 6-4-1 Structure of the Bobbin

Characteristics Required of the Material

To pass a current through the wire, it is necessary to remove the coating (urethane, etc.) at the end of the wire that is wrapped with the terminal. One way to peel off the coating is to dip it in a high temperature (300 to 400°C) solder bath.

For metal terminals, heat is not transferred to the bobbin even when dipped in a solder bath, so it is possible to use resin with relatively low heat resistance. For resin terminals, highly heat-resistant resin is needed so that the terminals do not melt or deform. However, with the recent miniaturization of home appliances, bobbins are also becoming smaller, and even if the terminal is metal, heat from short terminals is transferred to the resin portion. Therefore, heat resistant resin is needed. Because of this, high heat resistance (300°C to 400°C x several seconds) and precision molding are needed to achieve miniaturization, which are required characteristics of resin materials for bobbins. In addition, thermoplastic resins have been attracting attention because of environmental concerns, so LCP is often selected as a good material for bobbins.

Grade Selection Guide for Bobbin Applications

The super heat resistant grade E5000 series is best for resin terminal bobbins. The E5000 series can also be used for metal terminals, but the heat resistance may be excessively high. The E5000 series has high short-term heat resistance, but the molding temperature is also very high at 400°C and issues related to retention degradation in the injection molding machine can easily occur. The high-heat-resistant grade E4008 is our typical grade recommended for bobbins and coils. It has a heat resistance of 300°C or higher and has good moldability. It meets many standards such as UL746B in addition to UL94 V-0.
For metal terminal bobbins, it is recommended to select a grade from the E4000 series or E6000 series after considering the required heat resistance temperature and moldability for the bobbin.
E52008 is a high-flow grade of the ultra-heat-resistant grade E5008. It is good for bobbins with a wall thickness of 0.2mm or less such as ultra-small bobbins for stepping motors.

Table 6-4-1 Grades of SUMIKASUPER LCP for Bobbin Applications

Types of bobbins	Recommended grade
Plastic terminal bobbin	E5000 series (E5008L, E5008 etc.)
Metal terminal bobbin (small size)	E5000 series (E5008L, E5008 etc.) E4000 series (E4006L, E4008 etc.)
Metal terminal bobbin (medium and large)	E5000 series (E5008L, E5008 etc.) E4000 series (E4006L, E4008 etc.) E6000 series (E6006L, E6008 etc.)