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Through Hole Assembly
Through-hole assembly is a process used in printed circuit board (PCB) manufacturing where electronic components with wire leads (or “through-hole” leads) are inserted into holes on the PCB and then soldered in place. This method is especially used for components like connectors, switches, and other parts with leads that are meant to go through the PCB.
Through-Hole Assembly Process
Drilling Holes: The PCB is fabricated with holes at specific locations as defined by the PCB design. These holes are typically plated with copper to create electrical connections between layers.
Component Insertion: Electronic components with wire leads are manually or automatically inserted into the corresponding holes on the PCB. This can be done using automated insertion machines or by hand.
Bending Leads: If necessary, the leads are bent or formed to hold the components in place during soldering.
Soldering: The PCB is then passed through a wave soldering machine. This machine has a molten solder wave that makes contact with the exposed leads of the components, creating solder joints. The excess solder is removed, leaving clean connections.
Inspection: After soldering, the PCB is inspected for any soldering defects or issues with component placement. Automated optical inspection (AOI) and visual inspection are common methods.
Cleaning (Optional): If needed, the PCB may be cleaned to remove any flux residue left over from the soldering process.
Secondary Operations: Any secondary operations, such as trimming excess leads, may be performed.
Through-hole assembly is often used for components that require mechanical strength or high-reliability connections. It’s also suitable for components that generate a lot of heat, as the leads can act as heat sinks.
While surface mount technology (SMT) has largely replaced through-hole assembly for many applications due to its smaller size and cost-effectiveness, through-hole assembly is still used for specific components and applications where its strengths are preferred.
Through-hole Component Types
Through-hole components are electronic components with leads designed to be inserted through holes on a printed circuit board (PCB) for soldering. Here are some common types of through-hole components:
- Resistors:
- Fixed Resistors
- Variable Resistors (Potentiometers)
- Trimmers (Variable Resistors with adjustable value)
- Integrated Circuits (ICs):
- Operational Amplifiers (Op-Amps)
- Microcontrollers
- Analog/Digital Converters (ADCs/DACs)
- Logic Gates
- Inductors:
- Wire-Wound Inductors
- Ferrite Bead Inductors
- Potentiometers:
- Rotary Potentiometers
- Slide Potentiometers
- Sensors:
- Temperature Sensors
- Light Sensors
- Proximity Sensors
- Capacitors:
- Ceramic Capacitors
- Electrolytic Capacitors
- Tantalum Capacitors
- Film Capacitors
- Connectors:
- Headers
- Sockets
- Terminal Blocks
- Crystal Oscillators:
- Quartz Crystal Oscillators
- Ceramic Resonators
- Thermal Fuses:
- Safety Devices to protect against overheating.
- Filters:
- Common Mode Chokes
- LC Filters
- Diodes:
- Rectifier Diodes
- Zener Diodes
- Light Emitting Diodes (LEDs)
- Schottky Diodes
- Switches:
- Push-button Switches
- Toggle Switches
- Rotary Switches
- Transformers:
- Power Transformers
- Audio Transformers
- Buzzers and Speakers:
- Piezoelectric Buzzers
- Magnetic Speakers
- Crystals and Oscillators:
- Crystal Resonators
- Voltage-Controlled Oscillators (VCOs)
- Transistors:
- Bipolar Junction Transistors (BJTs)
- Field-Effect Transistors (FETs)
- Relays:
- Electromechanical Relays
- Solid State Relays (SSRs)
- Fuses:
- Blade Fuses
- Radial Fuses
- Terminals and Connectors:
- Screw Terminals
- PCB Mount Connectors
- Jacks and Plugs:
- Audio Jacks
- Power Plugs
These are just some examples of the various types of through-hole components. Each type serves a specific function in electronic circuits and systems. It’s important to select the appropriate component type based on the requirements of the circuit and the application.
Need Through Hole Assembly?
Are you in need of precise and reliable through-hole assembly for your electronic components? Look no further!
Our skilled team specializes in expert through-hole assembly, ensuring impeccable connections and robust performance. With our advanced equipment and meticulous craftsmanship, we guarantee top-quality results.
Our Strengths
1.Process Advantages
- For high-density mixed-technology boards:On double-sided mixed-assembly boards where the bottom side is already populated with heat-sensitive SMT components, selective soldering uses a miniature solder wave nozzle to jet solder only onto the designated through-hole pads. This eliminates the need for complex masking fixtures and fundamentally avoids the component heat damage, bridging, and solder ball risks associated with full-board immersion in wave soldering.
- For high-volume products with concentrated through-hole content: When the bottom side has no precision SMT components, wave soldering offers fast per-board cycle times and low per-unit cost, making it suitable for volume production in the tens of thousands of units.
- For simplified flow with a small number of through-hole components: When a board has only a few through-hole components, a stepped stencil can be used to print solder paste so that the through-hole components reflow together with the SMT components. This eliminates the separate wave soldering or selective soldering step, shortens the process flow, and reduces the number of thermal excursions.
2.Quality Reliability
- Benchmarking against core acceptance criteria: Meeting IPC standards (e.g., at least 75% barrel fill for Class 2/Class 3 product requirements), with solder joint geometry showing properly wetted concave fillets on both the top and bottom sides.
- Demonstrating process control and inspection capability: Selective soldering allows independent setting of soldering time and solder wave height for each individual joint, delivering good process repeatability and making solder joint reliability easier to control. In addition, X-ray inspection capability is in place to see through and inspect the internal fill condition of through-holes (voids, shrinkage pits) rather than relying on visual appearance alone. This meets the quality requirements of high-end electronic products such as automotive and medical devices.
3.Better mechanical strength
- Connectors and load-bearing components: Through-hole solder joints are formed by soldering the pins through the full board thickness, enabling them to withstand the mechanical stress of repeated insertion and removal.
- Power and heat-dissipating components: High-power resistors, transformers, and TO-package devices provide the necessary thermal mass and current-carrying paths through their through-hole pins.
- Long-term reliability in harsh environments: During thermal cycling, the through-hole pin structure better absorbs the thermal expansion mismatch between the PCB and the components, reducing the risk of solder joint cracking. This makes it suitable for industrial, automotive, and outdoor equipment.