Guide to Printed Circuit Board (PCB) assembly fabrication methods

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Guide to Printed Circuit Board (PCB) fabrication

The number of electronic devices which require a printed circuit board (PCB) is rising rapidly. Last month’s CES highlighted this with its scores of technical innovations. With each year, things become more and more elaborate and cutting-edge. Thus, printed circuit boards need to keep pace.

Electronic devices depend on high-quality PCBs to function safely, reliably, and efficiently. Popular devices like cell phones, TVs, and radios would be useless product shells without PCBs. Therefore, choosing an appropriate PCB assembly fabrication method plays a critical role in ensuring an electronic product’s success.

Learn more about PCB basics and printed circuit board assembly fabrication methods below.

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PCB Composition

Understanding PCB composition is important before choosing a fabrication method. Individual boards are made up of multiple layers as follows:

The substrate (or base material), is frequently made of FR4 fiberglass. One or more layers of copper are next. They act as a signal conductor on a completed PCB assembly.

Next, the solder mask insulates portions of copper which shouldn’t make contact with PCB assembly components. Finally, the silkscreen contains numbers, symbols, and indicators people working on the board will use during and after PCB assembly.

Important Terms

Understanding some basic electronics manufacturing terms is helpful, especially when trying to determine which type of printed circuit board is needed for a certain PCB assembly fabrication project. Common terms are listed below.

Drill Hit

The place where holes are drilled into the board. They should exactly match the design.

Pad

An exposed metal portion of the board on which components are soldered.

Plane

A continuous block of copper, defined by borders, also called a “pour.”

Reflow

A process in which joints are created between pads with solder.

Slot

Any hole in a PCB that’s not round. Slots may or may not be plated.

Surface Mount

Mounts which enable components to set on the board without needing leads to pass through it. Surface mount technology (SMT) is common in modern PCB manufacturing.

V-score

A partial cut through the board which allows circuit boards to be split into smaller pieces, for multiple PCB assembly pieces.

Fabrication Method Options

Multiple PCB assembly fabrication methods are used in the electronics industry today. Determining which one is right for a specific project depends on many different factors. To be effective, however, all methods require accurate, detailed designs.

Current (and common) fabrication methods are described below.

Etching

This easy, cost-effective fabrication method is reportedly one of the most common. Chemical solutions like ferric chloride or ammonium persulphate are used to remove excess copper from the board.

Manual

The PCB pattern design is manually drawn onto the board with this method.  Specialty pens or resist tapes are typically used.

Photographic

In this method, copper on a bare printed circuit board is covered with photo-resist material. An ultra-violet light is projected onto the board through photographic film or a photo mask, detailing required tracks. Track images are passed onto the photo-resist and then the board is submerged in a developer, so the affected material is removed.

Direct Etch

Laser printer toner can be used to make a direct etch resist via this fabrication method. The design is printed out on a laser printer and ironed directly onto a circuit board.

Silkscreen

This method is typically used by the largest PCB manufacturers. It is also used on the component side of the board to identify components, test points, PCB and PCBA part numbers, company logos, and more.

Final Finishes

Once PCB assembly fabrication is completed, a few finishing processes are required before the board is sent on for PCB assembly (usually to a separate location). These processes can include cleaning, tin plating, drilling, cutting, through plating and drawing a silkscreen legend.

PCB Manufacturing Considerations

Finding a manufacturer to meet PCB assembly demands is crucial. Several considerations should be made before choosing one. For instance, cost should be carefully weighed against quality, and a potential manufacturer should be able to meet all deadlines.

Material sourcing is also important. Bargain-hunting on materials could ultimately result in a PCB assembly quality sacrifice. Supplier consistency, adhering to safety regulations and supply chain restrictions can also impact manufacturing.

Finally, don’t be afraid to ask a manufacturer about certifications, equipment or one of these important questions. The answers could also have an important impact on a product’s success.