Understanding the PCB Assembly Process

Printed circuit boards live in every electronic device. PCB applications are enough to control the fuel economy in industrial equipment and nimble enough to direct search and rescue antenna instruments. It takes a lot of equipment, preparation, and investment to mass produce printed circuit boards. We would like to guide you through what investments, modifications, and processes looks like on an example PCB Assembly line.

How to Build Your High Volume PCB Facility

Before we even get to automated assembly, you must prepare your facility around the PCB assembly line. Have these environmental resources, secondary equipment, and support machines in place before you integrate a series of PCB Assembly machines. Expect to make capital investment in the space you will use before even getting started.

Part 1: The Facility Environment

Automated PCB Assembly requires a controlled environment. When planning the construction of your PCB assembly line, you’ll need to plan for space requirements, mitigate thermal stresses, and prevent contamination.

  • Manufacturing Space- A standard mass production line for PCB assembly requires a chain of interlocked machines. One high volume PCB assembly line can easily reach 50-80 feet. You are going to need at least that much space on your floor with additional side clearance for operator access. You will also need space for storage, testing equipment, and utilities.
  • Humidity Control- When working with sensitive electrical equipment, too much or too little moisture in the air can have a negative effect on PCB quality. Depending on your equipment, the ideal humidity ranges between 40%-60%.
  • Temperature Control- Excessive cold or excessive heat can damage components and prevent consistent quality across your boards. Keeping your assembly line facility between 65-75 degree Fahrenheit is recommended.
  • ESD Flooring- Even minor static can interfere with the quality of your PCB components. Paint, tiles, and even carpet can be designed with ESD. Placing anti-static flooring under and around the work envelope is a requirement for protecting your assembly line. Note: All ESD flooring has a shelf life and should be regularly tested for compliance and replacement.

Part 2: Storage Resources

You’ll need to manage and organize delicate parts and raw stock with limited shelf life. You’ll need to purchase a variety of inventory management equipment.

  • Fridge- Solder paste is a key ingredient necessary for permanent metal joining of parts to your PCB. You will need a large quantity of solder paste in storage at all times. With refrigeration, solder paste shelf life lasts roughly six months. Without refrigeration, your soldering paste will expire in roughly one month. Solder paste is expensive, but buying in bulk can alleviate some of the costs.
  • Component Storage Wire Racks- Organized safe storage of resistors, inductors, capacitors, transformers, potentiometers, transistors, diodes, integrated circuits, oscillators, switches, relays, and a variety of sensors is crucial when some of these components are as small as a flea. These wire racks allow easy cataloged access for your assembly team.
  • Dry Cabinets- Not every component can be stored in the open. These low humidity cabinets are necessary for sensitive electronic component storage.
  • Completed Assembly Storage Racks- You will need racks to store your finished boards. These racks are designed to eliminate static, resist chemicals, tolerate temperatures, and fit the dimensions of your PCBs.

Step 3: Power and Support Items

You will need specialized power and personal support items to accommodate the `

  • Electrical Drops- The average high volume PCB assembly line can have over a dozen interlocked machines. Voltage requirements on average range from 110V to 480V per machine. You will need grounded power access to run your assembly line.
  • Air Compressor- Multiple machines on the assembly line require air power and pneumatics to finish their portions of the PCB Assembly. Having a separate air compressor hookup is a requirement.
  • Nitrogen Gas System- High purity nitrogen gas is important to selective soldering. As an inert gas, it can reduce oxidization related defects and allow for more gradual temperature exposure when transferring PCBs further down the assembly line. You will need nitrogen tanks, generators, and dewars on site for PCB assembly.

Step 4: Personal Testing Equipment

Your team of engineers and PCB Assembly specialists need personal equipment to safely handle testing and manual selection of parts and boards.

  • Offline Station- Your electrical engineer needs a specialized workbench to functionally inspect and perform rework on individual boards. Expect to outfit this bench with a standard microscope and magnification light, manual soldering iron, and electrostatic dissipating (ESD) tools.
  • SMT and Selective Soldering Support Items- These range from tubes of specialty soldering paste, PPE, anti-fatigue floor mats, stencil wipes, under stencil roll papers, high temp gloves, ESD smocks, and other small touch up and inspection items useful to engineers and operators. 
  • Prototype Line- A smaller, shorter version of the high volume PCB line. These prototype lines allow for additional inspection, additional manual access, and manual testing and evaluation. While these prototype PCB assembly lines can also utilize pick and place, reflow, soldering, and other actions typical for the high volume line, their purpose is to prove prototype boards for efficient, cost effective, high volume production.

The High Volume PCB Assembly Line

You have created a prototype PCB Layout. You have refined the design for Design for Manufacturing (DFM), Design for Assembly (DFA), and Design for Testing (DFT) standards. You have prepared your work environment. You have assembled a series of automated machines to realize that mass production potential. You have loaded your reels of parts, refilled the soldering paste, loaded your panels of blank PCBs, hooked up your air, supplied your nitrogen, and activated power. You are ready for mass production.

Each PCB assembly line is going to be a little different. 

  • Some of the processes listed below may be combined in one machine. 
  • Assume there will be small linking conveyors between some machines. 
  • Assume all these machines have some form of internal conveyor capable of moving the PCB to the next stage. 
  • Assume that while there are dedicated testing machines on the line, each machine has its own quality control measures in place to minimize issues with production.

We are going to take you through an example high volume assembly line process that will cover all the basic technology you should expect on the line.

Step 1: Bare Board Loader

  • Vacuum cups, rollers, and drives in this machine select and carefully feed the PCB into the next machine with programmed orientation. 
  • Versions called Magazine Line Loaders can hold dozens of boards for automatic transfer to the PCB assembly line. 
  • Bare Board Loader machines can also have access for operators and ESD grounding receptacles.

Step 2: Screen Printer

  • This machine takes the bare boards and etches a ‘Legend’ of identifiers onto the silkscreen layer of the PCB. 
  • These references include part designations, test points, version identifiers, branding, and other touchstone markings that assist operators and automated equipment in the construction of PCBs.

Step 3: Solder Paste Dispenser

  • This machine takes your screen-printed PCB and overlays a stencil over the PCB so that only the areas that need solder paste are exposed. 
  • The machine then applies paste evenly over the stencil. 
  • The machine removes the stencil revealing a PCB precisely covered in solder paste over the marked areas for parts.
  • The machine finishes by cleaning the stencil of any leftover solder and moving the PCB to the next part of the assembly line.

Step 4: Solder Paste Inspection (SPI)

  • This machine uses 3D imaging software to scan your soldered and part free PCB. 
  • The machine checks for correct solder placement, too little solder, or too much solder. 
  • Approved PCBs move on to the next stage while flawed solder PCBs are marked for rework or disposal.

Step 5: Pick and Place

  • These machines hold the soldered PCB in place and precisely pick individual parts from reels of electric tape and places them onto the soldering points of the board. 
  • These machines can place thousands of parts per hour, accommodate parts of assorted sizes, and guide nozzles and grippers with laser guided sensors.

Step 6: Accumulation Conveyor

  • This conveyor allows controlled release of PCBs at certain stages of the assembly. 
  • This conveyor manages incoming supplies in the event of e-stop, manual inspection, defective board removal, or hand insert of parts.

Step 7: Inspection Workstation Conveyors

  • This conveyor runs through an operator workbench. 
  • Operators can hand insert specialty parts, make quality checks, or place or remove boards at this stage. 
  • While high volume PCB prohibits manual inspection of every PCB, this is another opportunity for quality control.

Step 8: Soldering Reflow Oven

  • While soldering paste will hold parts in place on the assembly line, your PCBs need permanent metal joining for every part. 
  • The reflow oven melts the soldering paste into permanent metal joints with precision temperature heating and cooling programming.
  • The reflow oven uses programmable temperature zones to manage application specific heating and cooling requirements.

Step 9: Cooling Buffer

  • Reflow ovens commonly reach 250 degrees Fahrenheit. 
  • The cooling buffer holds PCBs after coming off the reflow oven for controlled cooling. 
  • These machines use air, liquid, or hybrid cooling methods.

Step 10: 3D Automated Optical Inspection (AOI)

  • These machines use cameras and sensors to compare the finished physical PCB to programmed standards. 
  • They look for contamination, soldering flaws, damaged parts, board structure, part misplacement, and reference any number of customized testing points. 
  • They flag boards on a pass fail basis.

Step 11: Reject Conveyor

  • Typically placed after inspection stations
  • The reject conveyor machine automatically lifts flagged faulty boards off the conveyor for inspection/removal while allowing quality PCBs to pass through to the next stage.

Step 12: Magazine Line Unloader

  • This machine accepts finished boards off the conveyor and stores them in removable and transportable magazines. 
  • The boards then get moved to storage, delivery, or installation in embedded hardware products.

Post Processing Machines


We’ve shown you the essentials for your assembly line. These are post processing machines you might want to integrate into your PCB assembly line depending on your hardware needs.

PCB Flip Conveyors

  • If you want to install parts on both sides of the board, a PCB flip conveyor can automatically flip your PCB to the underside. 
  • The board can then go through the assembly process again for the reverse side only. 
  • These flipped PCBs may go through the same line or a separate specialty line.


  • Instead of assembling one PCB at a time, an assembly line can work with a panel of multiple attached circuit boards at once. 
  • Once the parts are attached and the boards are finished, this separate depaneling machine detaches the PCBs from the panel of circuit boards.

Additional Inspection

  • An In Circuit machine presses a bed of probes directly to the board to activate board components. 
  • Flying Probe machines use a high speed gantry to individually test parts on the board. 
  • An X-Ray Inspection machine can visually confirm board parts and layout on the inner layers of the board.
  • A Burn In testing machine stress tests the board for power consumption, environmental exposure, and maximum runtime.

Machine Tending

  • Mobile machine tending machines can be designed to refill reels of component tapes.
  • Machine tending machines can load and unload PCB magazines and individual boards.
  • Machine tending machines can automatically remove flagged boards from the production line.

Packaging and Palletizing

  • Packaging and palletizing machines manage singulation and orientation required to move PCBs from the assembly line to organized packing.
  • These machines can automatically label and seal your shipping packages.
  • They can stack your boxes on a pallet, wrap them, and load them for shipping.

High Volume PCB Assembly Contract Manufacturing

Every hardware product is different, and the technology needed to accommodate the variety of automated manufacturing and inspections methods doesn’t require personally investing millions of dollars in assembly equipment. Tell us more about your project, schedule a virtual meeting, or call (262)-622-6104 to learn how you can get started on high volume PCB assembly through DEVELOP LLC.