1. Connector basic features
High-speed transmission, heat dissipation, high-frequency testing, noise, power distribution, structure, appearance, environmental protection
2. Connector design concept
Light weight, miniaturization, small pitch, low cost, high performance, mass production
3. Design process
4. Plastic design skills
Plastic parts structure design - wall thickness design skills
4.1 Uniform thickness
4.2 The smallest possible thickness
4.3 There must be sufficient thickness at the bearing and welding to ensure product with a certain strength (Figure 1)
4.4 When the thickness is inconsistent, the molding will have shrinkage, bubbles, deformation and other undesirable phenomena.
4.5 Structural design of plastic parts — Design of reinforcement ribs and bosses
4.6 The principle of plastic material selection for connector design
The housing structure of the connector is basically thin (less than 0.02mm) with multiple pin holes and slender structure. Besides, the products from IT industry are constantly changed or updated fast. Thus, the choice of materials must follow below principles:
a. Good fluidity, products are formed in thin structure (such as LCP PBT NAYLON ......)
b. High strength and good impact resistance
c. High temperature resistance (SMT welding process requirements)
d. Excellent electrical performance (high insulation resistance, low dielectric constant)
e. Fast cooling speed (shorten the molding cycle, improve efficiency and save costs)
f. Under the satisfaction of its performance, try to choose as cheaper material as possible
5. Terminal parts design
The influencing factors of retention are as follows:
5.1. Retention design parameters include plastic selection, terminal tenon design, and interference design.
5.2. SMT TYPE CONNETORS must use high temperature resistant materials. (LCP NYLON PCT ... etc.)
5.3. There are generally two types of terminal positions: single-sided and double-sided. Each side can be designed with single-layer, double-layer and triple-layer designs.
5.4. The interference is usually designed (prior to 0.03 ~ 0.15mm), depending on the actual situation
5.5. The retention of plastic materials is in huge difference. Same design of tenon and interference but with different plastics will determine differences over 500gf;
5.6. Generally speaking, the retention of NYLON is greater than LCP, PCT is between the two, but the same LCP with different brands comes with big difference nearly 400gf;
5.7. The design of interference is better between 40µm ~ 100µm. (because the retention is not enough if the interference is less than 40µm. Over 100µm, the interference will not increase.) The interference between them increases its retention. With different chosen materials and tenon design, the difference of increase is about 30 ~ 120 (gf / 10µm).
5.8. The design drawing of the terminal tenon structure is as follows:
6. The influence to retention from tenon structure
6.1. The length of the bump is related to the retention force. The longer the length, the greater the retention.
6.2. Single-sided tenon has greater retention force than bilateral
6.3. The retention of double convex points is greater than that of single convex points, but it is not obvious and can be ignored
6.4. The bump angle is independent of the retention force
6.5. The thinner plate is relatively low on retention
6.6. In summary, the larger the contact surface between the terminal and the plastic, the greater the retention force. The effect is obvious.
6.7 Terminal normal force design
a. Normal force of gold-plated terminals: 50 ~ 150gf
b. The normal force of the tinned terminal must be greater than 150gf
c. The normal force is absolutely related to product reliability;
d. The normal force is closely related to the contact resistance;
e. PIN amount greater than 200 moderately reduces the normal force;
f. There is a relationship between normal force and operation;
g. The normal force is closely related to the instant interruption of the vibration test. Increasing the normal force improves the problem of instant interruption;
h. The normal force will seriously affect the abrasion resistance of the plating layer.
i. Plated terminals and contact resistance compared to permanent deformation and normal force
j. The permanent deformation is affected by the maximum stress value of FEM, that is, the stress concentration will cause permanent deformation
k. The permanent deformation will not decrease normal force of the terminal, but an increase in the terminal (normal force, displacement).
l. When the theoretical stress value of the terminal is greater than the strength of the material, the number of repeated pressures fail to reach 10,000 times, the higher the stress, the lesser it reaches. When the stress value exceeds 1.8 times the maximum value, it remains 2000 cycles.
m. If the stress value of a designed product is higher than the material strength, it is easy to confront embrittlement.
7. Basic requirements to the selection of terminal copper material:
7.1 Low contact resistance and material resistance to meet circuit requirements
7.2 Corrosion resistance must be low
7.3 When it is inserted firmly, it must have low friction and good conductivity
7.4 Appropriate flexibility characteristics
7.5 Low price
7.6 Conductivity: minimum material resistance
7.7 Extensibility: terminal forming
7.8 Adjusted strength: within flexible range, it has large displacement
7.9 Stress relief: the terminal still maintains its resistance to load long-term stress or high temperature
7.10 Hardness: reduces terminal metal abrasion
7.11 Common materials: brass-low price, good conductivity, poor mechanical strength; phosphor bronze-medium price, slightly poor conductivity, good mechanical strength; beryllium copper-high price, good conductivity and mechanical strength.
7.12 Molding characteristics of terminal materials:
As the strength of the alloy increases, the moldability decreases.
The minimum bending radius, the inner R> = 1 times the thickness of the copper plate material.
The material stamping characteristics. The direction and geometric characteristics.
7.13 Demonstration diagram of terminal structure: