In the realm of electronic connectors, the selection of plastic materials for both housings and headers is pivotal for ensuring functionality, safety, and longevity. This post delves into the common materials used, their characteristics, and their suitability for specific applications, drawing from industry standards and manufacturer specifications.
Connector housings and headers serve distinct roles within electronic systems: housings provide mechanical support and electrical insulation for contact members, while headers, particularly those soldered onto printed circuit boards (PCBs), must endure high-temperature processes like reflow soldering. The choice of material impacts heat resistance, mechanical strength, electrical insulation, and cost, making it essential to align material properties with application requirements.
Common Plastics for Connector Housings
Connector housings, used in wire-to-wire and wire-to-board systems, typically are made in Nylon 66 (PA66) and PBT (Polybutylene Terephthalate).
Nylon 66 (PA66)
Nylon 66 is a polyamide with high tensile strength, typically ranging from 80-100 MPa, and excellent heat resistance, with a heat deflection temperature (HDT) at 1.8 MPa of approximately 230-260°C for standard grades. Its melting point is around 260-270°C, making it suitable for high-temperature processes. It is flame-retardant, often rated UL 94V-0 or UL 94V-2, ensuring safety in electrical applications. However, it has moderate moisture absorption (1-3%), which can affect dimensional stability in humid environments. Its chemical resistance is good against hydrocarbons but fair against acids and bases.
PBT (Polybutylene Terephthalate)
PBT is a thermoplastic polyester with good mechanical strength, typically 50-70 MPa in tensile strength, and dimensional stability due to low moisture absorption (0.1-0.5%). Its standard HDT at 1.8 MPa is around 170-200°C, with a melting point of 220-230°C. Heat-stabilized grades can achieve HDT up to 220°C, making them viable for some connector applications. PBT offers excellent chemical resistance to acids, bases, and hydrocarbons, and flame-retardant grades are available with UL 94V-0 ratings.
Comparative Analysis
| Property | Nylon 66 (PA66) | PBT |
|---|---|---|
| Heat Deflection Temperature (°C) | 230-260 | 170-200 (standard), up to 220°C (stabilized) |
| Tensile Strength (MPa) | 80-100 | 50-70 |
| Moisture Absorption (%) | 1-3 | 0.1-0.5 |
| Flame Retardancy | UL 94V-0/94V-2 | UL 94V-0 (with additives) |
| Chemical Resistance | Good (fair against acids/bases) | Excellent (acids, bases, hydrocarbons) |
| Cost | Higher | Lower |
Common Plastics for Connector Headers (PCB-Soldered)
Common materials for connector headers include PBT, PA66, PA6T, PA9T, and LCP. PBT and PA66 are typically used for through-hole type headers due to their temperature resistance, while PA6T, PA9T, and LCP are frequently employed for SMT headers, as they are well-suited for the reflow soldering process.
LCP (Liquid Crystal Polymer)
LCP offers exceptional heat resistance, with an HDT up to 300°C, low thermal expansion, and high dimensional stability. It excels in electrical properties, with tensile strength around 150-200 MPa, and has almost zero moisture absorption, ensuring excellent dimensional stability. It is flame-retardant, typically rated UL 94V-0, and offers excellent chemical resistance.
PA6T (Nylon 6T)
PA6T, a semi-aromatic polyamide, offers enhanced heat resistance with an HDT of 270-290°C, surpassing PA66. It has tensile strength similar to PA66, around 80-100 MPa, and lower moisture absorption (1-2%) compared to PA66. It is flame-retardant, often rated UL 94V-0 or UL 94V-2, and has good to excellent chemical resistance, better than PA66 due to its semi-aromatic structure.
PA9T (Nylon 9T)
PA9T, another high-performance polyamide, provides superior heat resistance (HDT up to 290°C), excellent toughness, and low moisture absorption (0.5-1%). Its tensile strength is higher than PA66, around 100-120 MPa, and it is flame-retardant, rated UL 94V-0 or UL 94V-2. It offers good to excellent chemical resistance, similar to PA6T, and is designed for extreme conditions.
PA66
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PBT
Check above.
Comparative Analysis
| Material | HDT (°C) | Tensile Strength (MPa) | Moisture Absorption (%) | Flame Retardancy | Chemical Resistance | Cost |
|---|---|---|---|---|---|---|
| PA66 | 230-260 | 80-100 | 1-3 | UL 94V-0/94V-2 | Good | Medium |
| PBT | 220-240 | 50-70 | 0.1-0.5 | UL 94V-0 | Excellent | Low |
| LCP | up to 300 | 150-200 | almost 0 | UL 94V-0 | Excellent | Very High |
| PA6T | 270-290 | 80-100 | 1-2 | UL 94V-0/94V-2 | Good to Excellent | High |
| PA9T | up to 290 | 100-120 | 0.5-1 | UL 94V-0/94V-2 | Good to Excellent | High |
Conclusion
The choice of plastic materials for connector housings and headers significantly affects their performance and reliability. Nylon 66 (PA66) and PBT are commonly used for housings and through-hole type headers, providing a mix of strength and affordability. In contrast, LCP, PA6T, and PA9T are typically selected for SMT (surface-mount technology) headers, meeting the diverse demands of high-temperature and challenging environments. Understanding these material properties ensures connectors achieve the required standards for safety, durability, and functionality.