Introduction
Terminals are the core functional components of connectors, bearing the critical roles of electrical conduction and mechanical connection. The quality of terminals directly determines the contact reliability, current-carrying capacity, and service life of connectors. Terminal manufacturing is mainly accomplished through precision stamping processes. From raw materials to finished terminals, multiple precision processing steps and strict quality control are required. This article provides an in-depth analysis of the stamping manufacturing process of connector terminals and its quality control points from the perspective of the entire process, including material selection, tooling design, stamping process, and electroplating treatment.
1. Terminal Materials: The Foundation and Source of Performance
The selection of terminal materials is the first step in terminal manufacturing and also the foundation determining terminal performance. Different application scenarios have different performance requirements for terminal materials, including conductivity, elasticity, strength, corrosion resistance, heat resistance, and solderability.
Common Terminal Materials and Their Characteristics
Brass: A copper-zinc alloy and one of the most commonly used terminal materials. Brass has good conductivity and processability with relatively low cost. However, its elasticity is average, and its stress relaxation resistance is poor, making it unsuitable for contact springs with high elasticity requirements. Brass terminals are commonly used for structural parts such as pins and leads that do not require high elasticity, or for contact parts in cost-sensitive products. Common grades include C2680 (65/35 brass), C2600 (70/30 brass), etc.
Phosphor Bronze: A copper-tin alloy with a small amount of phosphorus added to improve performance. Phosphor bronze has better elasticity and strength than brass, good fatigue resistance, and good conductivity, making it the mainstream material for terminal contact parts. It is widely used in elastic contact parts such as spring pieces and jacks of various connectors. Common grades include C5191, C5210, etc. The higher the tin content, the better the strength and elasticity, but with a slight decrease in conductivity.
Beryllium Copper: A copper-beryllium alloy and one of the most excellent elastic copper alloys. Beryllium copper has extremely high strength, elasticity, and fatigue resistance while maintaining good conductivity and corrosion resistance. After aging heat treatment, its elasticity and strength can reach very high levels. Beryllium copper is mainly used for connectors with high reliability requirements, such as automotive connectors, military connectors, high-speed connectors, etc. However, beryllium copper is expensive, and beryllium has certain toxicity, requiring special protection during processing. Common grades include C17200, C17410, etc.
Titanium Copper: A copper-titanium alloy and a high-performance elastic copper alloy. The elasticity and stress relaxation resistance of titanium copper are close to beryllium copper, and it does not contain beryllium, making it more environmentally friendly and safe. In high-temperature environments, the elasticity retention of titanium copper is better than phosphor bronze. In recent years, with the increasing demand for beryllium copper alternatives, titanium copper has been increasingly widely used. Common grades include C1990, C1995, etc.
Nickel Silver/Copper-Nickel-Zinc Alloy: Has good corrosion resistance and elasticity, with a silvery-white appearance, and in some cases can eliminate the need for nickel plating. However, conductivity is relatively poor, mainly used in specific application scenarios.
Material Selection Considerations
When selecting, the following factors need to be comprehensively considered:
- Conductivity: For applications with high current-carrying requirements, prioritize materials with high conductivity.
- Elasticity and Stress Relaxation: For elastic parts that need to maintain contact normal force for a long time, materials with good elasticity and stress relaxation resistance should be selected, such as beryllium copper, titanium copper, or high-tin phosphor bronze.
- Operating Temperature: In high-temperature environments, the elasticity of materials will decay, requiring alloys with good high-temperature performance.
- Corrosion Resistance: In corrosive environments, materials with good corrosion resistance need to be selected, or matched with appropriate surface plating.
- Cost: On the premise of meeting performance requirements, prioritize lower cost materials.
- Processability: Different materials have different stamping and electroplating properties, which need to be matched with the manufacturing process.
2. Stamping Dies: The Process Core of Precision Terminals
Terminal stamping is the process of processing metal strips into terminals of specific shapes through dies. The design and manufacturing level of dies directly determine the precision, quality, and production efficiency of terminals. The dimensional accuracy of precision connector terminals usually requires plus or minus 0.01mm or even higher, imposing extremely strict requirements on dies.
Progressive Dies and Stamping Processes
Almost all connector terminals are produced using progressive dies. A progressive die arranges multiple stamping processes in sequence in a single die. The metal strip is fed from one end and gradually processed through each station, finally obtaining finished terminals at the discharge end. This production method has high efficiency and good consistency, suitable for mass production.
A typical terminal stamping progressive die includes the following main processes:
1. Piercing/Blanking: Punching process positioning holes and initial outline contours on the strip. The positioning holes are the reference for precise positioning of subsequent stations, and their accuracy directly affects the dimensional accuracy of the entire terminal.
2. Outline Blanking: Gradually punching out the outer contour of the terminal, including the terminal head, tail, elastic arm, and other structures. Complex terminal outlines usually require multiple blanking steps to avoid excessive deformation or burrs caused by one-time blanking.
3. Bending Forming: Bending the blanked blank into the required three-dimensional shape, such as elastic arm bending, pin bending, etc. Bending is one of the most critical processes in terminal stamping. The control of bending angle and springback directly affects the assembly and performance of the terminal.
4. Sizing/Coining: Finishing the bent terminal, correcting springback, and ensuring dimensional accuracy meets requirements.
5. Cutting/Parting Off: Separating the formed terminal from the strip. Some terminals remain on the strip (strip-fed terminals) for subsequent electroplating and assembly; others are directly dropped as individual terminals.
Key Control Points in Die Design and Manufacturing
1. Stamping Clearance: The clearance between the punch and die is one of the most important parameters in the blanking process. Too small clearance leads to increased burrs and accelerated die wear; too large clearance leads to poor section quality and large rollover. The blanking clearance for precision terminals is usually controlled between 3% and 8% of the material thickness, with specific values determined based on material and thickness.
2. Positioning Accuracy: The step accuracy and positioning accuracy of progressive dies directly affect the dimensional consistency of terminals. Common positioning methods include pilot pin positioning, stock guide positioning, etc. Precision dies use high-precision pilot pins with positioning accuracy of up to plus or minus 0.005mm.
3. Bending Springback Control: Metal materials will produce elastic springback after bending, causing deviations in bending angle and dimensions from design values. During die design, the springback amount needs to be considered in advance, compensated through over-bending, sizing, and other methods. Different materials have different springback characteristics, requiring specific compensation amounts determined through experiments and simulation.
4. Die Materials and Heat Treatment: Working parts of precision stamping dies usually use high-performance materials such as high-speed steel, powder metallurgy steel, or cemented carbide, and undergo strict heat treatment to ensure die hardness, wear resistance, and service life. Die life is an important factor affecting terminal production costs.
5. Guide Accuracy: Progressive dies usually use high-precision guiding mechanisms such as ball guide pillars and bushings to ensure the alignment accuracy of upper and lower dies. Guide accuracy directly affects the uniformity of blanking clearance and the dimensional accuracy of terminals.
3. Stamping Process: Process Control Determines Product Quality
With good materials and good dies, precise stamping process control is also required to produce high-quality terminals. Process parameter control and quality monitoring during the stamping process are key links to ensure product quality.
Stamping Equipment Selection
Precision terminal stamping requires the use of high-precision presses. Common types include high-speed precision presses and servo presses:
High-Speed Precision Presses: High stroke rates (up to hundreds or even thousands of strokes per minute), good rigidity, stable precision, suitable for mass production of standardized products.
Servo Presses: Driven by servo motors, they can precisely control the motion curve of the slide, with adjustable stamping speed and stroke, suitable for stamping complex shapes and difficult-to-form materials. Although not as fast as high-speed presses, the forming quality is better, and process adaptability is stronger.
The precision of the press mainly includes: parallelism, perpendicularity, total clearance, bottom dead center repeat accuracy, etc. The requirement for bottom dead center repeat accuracy of the press for precision terminals is usually within plus or minus 0.005mm.
Key Process Parameter Control
Feeding Accuracy: The accuracy of the feeding step pitch directly affects the positioning accuracy of the progressive die. Precision stamping usually uses roll feeders or gripper feeders, with feeding accuracy within plus or minus 0.01mm. Tension control of the strip is also important, as tension fluctuations can affect feeding accuracy.
Stamping Speed: Different materials and processes have different optimal stamping speeds. Too high a speed may cause material cracking due to insufficient deformation time, or intensified die heating; too low a speed results in low production efficiency. The appropriate stamping speed needs to be selected based on product characteristics and material properties.
Material Condition: Before stamping, it is necessary to check whether the raw material’s thickness tolerance, hardness, surface quality, etc. meet requirements. Material quality fluctuations directly affect stamping quality and die life.
4. Electroplating Treatment: Surface Performance and Long-Term Reliability
Electroplating is the post-processing step for terminal manufacturing, which improves the corrosion resistance, conductivity, weldability, and wear resistance of terminals through surface coating treatment. The plating quality directly affects the long-term reliability and appearance quality of connectors.
Common Plating Types and Applications
Tin Plating: The most common plating type, with good solderability and low cost. Suitable for general industrial and consumer electronic products. Mainly used for welded ends and general contact areas. However, tin is prone to oxidation and tin whisker growth, requiring attention to usage scenarios.
Gold Plating: Excellent corrosion resistance and low and stable contact resistance. Suitable for high-reliability occasions such as weak signal transmission, high-frequency applications, and harsh environments. Gold plating is usually divided into flash gold, hard gold, thick gold, etc., selected according to performance requirements. Gold plating is widely used in high-end connectors such as communications, medical, automotive, etc.
Nickel Plating: Usually used as an undercoat or intermediate layer. As a diffusion barrier between the base material and the surface coating, it prevents copper atoms from diffusing into the gold or tin layer, improving coating adhesion and corrosion resistance.
Silver Plating: Has the highest conductivity among common metals, suitable for high-current and high-frequency connectors. However, silver is prone to oxidation and sulfuration, resulting in unstable contact resistance, requiring use with protective measures.
Electroplating Process Quality Control Points
1. Plating Thickness: Plating thickness is the most basic quality indicator of electroplating. Insufficient thickness leads to reduced protective performance and poor contact; excessive thickness increases costs and may cause dimensional deviation. Different applications have different requirements for plating thickness. Generally, industrial tin plating of 3-5 micrometers is sufficient, and gold-plated contact areas are usually 0.1-0.8 micrometers.
2. Plating Adhesion: There must be good adhesion between the coating and the substrate, otherwise problems such as coating peeling and blistering may occur during use. Adhesion is usually tested through bending, thermal shock, and other tests.
3. Plating Uniformity: The thickness distribution of the plating should be uniform, avoiding local thinning or thickening. Rack design, current distribution, additives, etc. in the electroplating process all affect plating uniformity.
4. Solderability: For terminals that need to be soldered, the solderability of the plating is a key indicator. Usually evaluated by wetting balance method or tin immersion test.
5. Porosity: The porosity of the coating directly affects corrosion resistance. Too high porosity leads to substrate corrosion and reduces product life.
6. Selective Plating Control: Many connector terminals use selective plating processes, gold plating only in the contact area and tin plating in other areas. The position accuracy and boundary clarity of selective plating are important quality control points.
5. Full-Process Quality Assurance System
The production of high-quality terminals cannot be separated from a complete quality assurance system:
Incoming Quality Control (IQC): Strict factory inspection of raw materials (copper strips, electroplating chemicals, etc.) to ensure raw material quality meets requirements.
In-Process Quality Control (IPQC): Patrol inspection and spot check during stamping and electroplating production processes, to promptly discover and correct process deviations.
Final/Outgoing Quality Control (FQC/OQC): Comprehensive quality inspection before finished products leave the factory, including multiple dimensions such as size, appearance, electrical performance, mechanical performance, etc.
Reliability Verification: Regular product reliability testing, such as salt spray test, mating/unmating life test, temperature rise test, contact resistance test, etc., to ensure long-term product reliability.
Conclusion
The manufacturing of connector terminals is a systematic project. From material selection to die design, from stamping process to electroplating treatment, every link is crucial. Materials are the foundation of performance, dies are the core of the process, stamping process control determines dimensional accuracy and consistency, and electroplating determines surface performance and long-term reliability. Only through strict control throughout the entire process can high-quality, high-reliability connector terminals be produced.
RXSY has established a complete terminal stamping and electroplating quality control system, checking layer by layer from raw materials to finished products to ensure each terminal meets high-quality standards. For more information on terminal manufacturing processes and connector products, please refer to the RXSY product series. We provide reliable connection solutions for customers with precision manufacturing and strict quality control.
