PCB News - SMT connector uses nylon 6T and LCP plastic comparison

SMT connector uses nylon 6T and LCP plastic comparison

When the company’s products introduced the [Flip Lock connector], the product value problem of the flip cover/actuator fracture occurred, some of which were the pivot fracture of the movable cover. Compare The more serious case is that the whole movable cover is broken; and some are broken at the place where the connector housing itself bears the pivot of the movable cover. Later, although the connector manufacturer changed the plastic material from the original Nylon 6T to LCP, because this was the simplest method and didn't need to spend too much money. Although the defect rate has been improved, it has not been completely resolved. But this only shows that LCP material is stronger than nylon 6T.

However, what we are going to talk about today is not how to solve the problem of connector fracture, but to talk about the comparison and applicability of nylon 6T and LCP engineering plastic materials used by many circuit board manufacturers in SMT connectors, especially Used in clamshell or board-to-board connectors.

Nylon 6T (Nylon 6T)
The melting point of modified Nylon6T (hereinafter referred to as nylon 6T) usually falls around 310~320°C. The melting point in such a range makes it easy to use an injection molding machine to process without causing degrade, and still has excellent temperature resistance. The HDT (heat distortion temperature) of some nylon 6T can reach 290~300°C, which is quite suitable for the use of SMT connector materials.

The main characteristics of nylon 6T are high temperature resistance, high strength, good creep resistance, excellent dimensional stability, less burrs during processing and molding, and its composition (modification) can be adjusted to suit the required performance.

The disadvantage of nylon 6T is that it will absorb a little water, which will affect the stability of high-temperature dimensions after absorbing water, so try to avoid exposure to the atmosphere to absorb too much water. In addition, nylon 6T itself has poor flame resistance. To make it pass UL94V-0, flame retardants must be added. Because most flame retardants produce corrosive substances, the materials of processing equipment must be corrosion-resistant. The injection mold must also be treated with rust prevention regularly. Generally speaking, if the grade can be selected appropriately, nylon 6T can be said to be an excellent material for SMT connectors. The processing temperature of nylon 6T is high (320-330°C).

LCP (Liquid Crystal Polymer, liquid crystal polymer)
Generally speaking, LCP materials have good mechanical properties, even without adding glass fiber (GF, Glass Fiber), they can show the mechanical strength equivalent to that of general engineering plastics with glass fiber added. If GF is added, the strength is better than general engineering plastics. Another advantage of the mechanical properties of LCP is that it is heat resistant and can exhibit good mechanical strength even at high temperatures. Depending on the HDT capability of different levels, LCP can be used continuously at temperatures below 230-300°C. Detract from its characteristics.

LCP also has good chemical resistance, weather resistance, radiation resistance, and excellent flame retardancy. It can automatically extinguish the flame without continuous combustion or spontaneous combustion. LCP also has excellent insulating properties, and its dielectric strength (dielectric) is much higher than that of general engineering plastics.

Although its molecular orientation can increase the strength of LCP, it also forms anisotropy, which means that plastics in different directions will have different physical properties, and some places will also form weak points. For precise SMT connections The finished product is a very unfavorable factor. However, after adding glass fiber (GF), the molding anisotropy of LCP can be reduced. If a little attention can be paid to the improvement of the mold design, the weak points can be overcome.

In addition, the welding strength (Welding Srength) of LCP is low, so special care must be taken when designing the mold, so that the welding line (Welding line) should not appear in the stressed place.

If purely in terms of material characteristics, regardless of price, LCP can be said to be a very good SMT connector material, and for RoHS parts that require a higher heat resistance temperature to pass through Reflow, LCP can maintain its stability at high temperatures. There is no problem of dimensional instability of Nylon 6T after moisture absorption. (Explained by circuit boardmanufacturer)