Printed circuit board (PCB) assembly is the process of soldering electronic components to a PCB. This allows the creation of a functional electronic circuit. There are various machines and equipment used in PCB assembly to automate the production process. The main machines include soldering machines, inspection machines, material handling equipment, cleaning equipment and more.
Selecting the right PCB assembly equipment is crucial to achieving high productivity, quality and yield. The choice of machine depends on factors like:
- Type of components to be soldered
- Production volume
- Required precision and accuracy
This article provides a comprehensive overview of the different types of machines used in PCB assembly and discusses their features, working principles, advantages and typical applications.
Soldering is the most important step in PCB assembly. It involves melting solder to create permanent joints between component leads and PCB pads. The main types of soldering machines are:
Wave Soldering Machine
- Solder pot – Contains molten solder alloy
- Pump – Generates the solder wave
- Preheating stage – Preheats the PCB to ensure proper soldering
- Fluxer – Applies flux to PCB before soldering
- Conveyor – Transports PCB through the machine
Wave soldering is ideal for soldering through-hole components on mass production PCBs. It allows high throughput up to thousands of boards per hour. However, it is not suitable for soldering surface mount devices (SMDs).
Reflow Soldering Oven
A reflow soldering oven uses heat to melt solder paste and form solder joints between SMDs and PCB pads. The oven has multiple heating zones with increasing temperatures to heat up the board. The stages are:
- Preheating – Slowly heats up the board to evaporate solvents from solder paste
- Reflow – Heats the board above the melting point of solder to form joint
- Cooling – Cools the board down to solidify solder
For small volumes, reflow ovens with infrared heating are used. For mass production, convection ovens with forced air circulation provide faster heating. The peak temperature is around 217°C.
Reflow ovens allow excellent soldering quality and are ideal for SMD assembly. However, cycle times are longer compared to wave soldering.
Selective Soldering Machine
A selective soldering machine solders specific parts on the board using a miniature solder wave or solder fountain. It has a solder pot, pump, fluxer and conveyor. The key difference from wave soldering is:
- Soldering head – A precision soldering nozzle that selectively applies solder only where needed.
Selective soldering provides flexibility to solder both through-hole and SMD components. It is ideal for manual rework or soldering heat-sensitive components after reflow.
Inspection of solder joints and checking for defects is vital in PCB assembly. Common inspection machines include:
Automated Optical Inspection (AOI)
AOI machines use high resolution cameras to visually inspect the quality of solder joints. They use pattern recognition software to compare the PCB to a known good reference.
AOI provides fast and accurate inspection immediately after soldering. Both solder joints and component placement can be checked. However, it may not detect subtle flaws.
X-ray inspection provides very detailed inspection. However, the equipment is more expensive than AOI. It is better suited for small boards.
Flying Probe Tester
This machine uses two movable “flying” probes to electrically test PCBs for shorts, opens, resistance and functionality. The probes move over the board and make contact with test points.
Flying probe testing verifies PCB assembly and detects manufacturing defects. It replaces fixture-based testing for small volumes.
Material Handling Equipment
Efficient material handling improves productivity in PCB assembly. Common material handling equipment includes:
Conveyors are used to automatically transport PCBs between different assembly machines. This avoids manual material handling.
Automatic Solder Paste Printer
This machine uses stencils to apply the solder paste pattern onto the PCB before reflow soldering. It improves repeatability and reduces application defects.
Automatic Component Placer
This rapidly picks components from feeders and accurately places them on defined positions on the board. It avoids manual placement and improves quality.
After soldering, flux residue remains on the PCB which can be corrosive and conductive. Cleaning is essential. Common cleaning equipment:
Washers use liquids like deionized water to remove flux and other contaminants from the PCB surface. Different types include batch washers, inline washers, ultrasonic washers etc.
Specialized cleaning agents like alcohols, solvents and detergents are used for effective PCB cleaning prior to washing.
Dryers like centrifugal dryers are used to completely dry the PCB after washing to avoid any residual moisture.
Manual rework stations may be needed to repair defective boards or replace components. This allows recovery of PCBs instead of scrapping them. Common rework equipment includes:
Soldering & Desoldering Stations
Manual soldering/desoldering tools allow localised repair of solder joints without affecting the complete board. Hot air jets, infrared preheaters and vacuums ease the rework.
Fume Extraction Systems
Fume extractors remove harmful flux fumes released during rework soldering/desoldering. This improves operator safety.
ESD Control Equipment
Wrist straps ground the operator to safely discharge any static buildup.
Conductive mats prevent electrostatic charge generation during handling and assembly.
Ionizers neutralize electrostatic charges by emitting positive and negative ions in the surroundings.
ESD Containers & Packaging
Components are stored and transported in static shielding bags and ESD certified containers.
Some other auxiliary equipment required:
- Storage racks for PCBs, components and materials
- Workbench, chairs and tools for manual workstation
- Solder wire, solder bars, fluxes, cleaning agents
- Computer and software for production monitoring
- Label printer for product identification
- Measurement & testing equipment (microscopes etc.)
- Fire extinguisher, first aid kit & PPE
Factors for Selecting PCB Assembly Equipment
The main factors guiding PCB assembly machine selection:
The production rate or number of boards that can be processed per hour. High throughput equipment like wave soldering and placement machines are needed for mass production.
The dimensions of the PCBs being assembled. Large boards will need wider conveyors and large ovens.
Through-hole, SMD or mixed? The component package types impact the soldering methods required.
Accuracy & Repeatability
Precision assembly demands machines with high accuracy, precision placement and consistent process control.
Flexibility to switch between different PCB products, varying placement programs etc improves utilization.
Both equipment purchase cost and ongoing operating costs should be affordable.
The floor space available in the production facility for accommodating the machines.
Operator Skill Level
Automated machines reduce dependency on operator skills. But rework still needs skilled operators.
Recommended Basic Setup
A basic setup for low volume PCB assembly could include:
- Reflow oven for SMD soldering
- Selective soldering machine for THD components
- Automatic solder paste printer
- Small component placement machine
- AOI inspection system
- Cleaning equipment like washer, dryer etc.
- Rework station with microscope
- Fume extraction system
- ESD control equipment
- Conveyor system for material handling
Whereas a setup for high volume manufacturing would include:
- Wave soldering machine
- Large reflow oven
- High speed component placer
- 2-3 AOI machines (pre-reflow and post-wave)
- X-ray inspection system
- Industrial washing systems
- Automatic storage & retrieval systems
- Extensive conveyor links between machines
- Testing systems & flying probers
Main Suppliers of PCB Assembly Equipment
Some leading global suppliers of PCB assembly equipment include:
- ASM – SMT placement, soldering and inspection systems
- Juki – SMT assembling machines (placers, printers etc.)
- Yamaha – Surface mount machines, bonders, printers
- Panasonic – SMT production solutions
- Europlacer – High speed, high precision component placers
- Mycronic – Dispensing, jetting, placement and AOI
- Nordson – Soldering (selective, wave) and dispensing systems
- Vitronics Soltec – Wave and selective soldering machines
- Asscon – Soldering machines (reflow, wave, selective)
- Zymet – SMT screen printers, dispensers and placers
- Manncorp – Reflow ovens,selective soldering and more
- CTC – Conveyor systems for SMT production lines
- Aqueous Technologies – PCB cleaning equipment
- MPI – Automated optical inspection (AOI) machines
- Viscom – 3D AOI and X-ray inspection systems
- Takaya – Flying probe PCB test equipment
- PACE – Manual soldering stations, fume extractors
Choosing suppliers with extensive experience, proven machine quality and responsive service support ensures long term equipment performance.
This covers the major types of PCB assembly machines and equipment currently used in the electronics manufacturing industry. The right set of machines with matching production volumes, PCB types, accuracy needs and budget ultimately enables efficient and quality PCB assembly. With numerous suppliers available globally, manufacturers can build an optimized production line meeting their exact requirements. By adopting more automation and smart manufacturing principles, PCB assembly facilities can reap benefits like higher throughput, improved quality, lower costs and greater reliability in electronic device production.
What are the main steps in PCB assembly that require machines?
The four main processes in PCB assembly that use machines are:
- Solder paste printing
- Component placement
- Soldering (reflow or wave)
- Inspection by AOI/x-ray
Additional processes like flux application, cleaning, testing etc. may also use equipment.
What is the difference between pick and place and component placement machines?
Pick and place broadly refers to machines that pick components and place them on PCBs. However, in PCB assembly, component placement machine or SMT pick-and-place machine refers to the more sophisticated, high-speed, high-accuracy machines used.
How are large PCBs assembled if they cannot fit in SMT machines?
For large PCBs, manufacturers use modular SMT lines consisting of multiple smaller linked machines. Large PCB panels are divided into individual boards that pass through the machines separately before being panelized again. Conveyor systems link the machines.
When should AOI vs X-ray inspection be used in PCB assembly?
AOI provides a fast, low-cost inspection solution in most cases. X-ray inspection is more thorough in detecting hidden defects but costs much higher. X-ray is recommended for high reliability boards or periodically instead of inspecting every board.
What is the typical soldering temperature used?
For reflow soldering, the peak temperature is around 217°C depending on the solder alloy used. Wave soldering requires higher temperatures of 255-265°C for the solder to remain molten.
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