If you're interested in pursuing in-house PCB prototyping and testing, there are several routes you can take to create functional prototypes for new products. The best one depends on a number of factors, with product complexity being the primary consideration. For highly complex, low-volume products, using an additive manufacturing system is often the best choice for rapid prototyping thanks to its high throughput and fixed cost structure.

In-House PCB Prototyping Over Time

Although PCBs have been around since the early 20th century, their manufacturing and in-house prototyping methods were not always standardized. In 1936, the first PCB was used to support an electronic system, and the prototyping process was not significantly different from the manufacturing process in those early days.

As fabrication and electronic component technology has progressed over time, so have the available options for in-house PCB prototyping. The story of in-house PCB prototyping methods can be traced back to the 1960s when electronics were making the transition from vacuum tubes to transistors. At this point, a large metal chassis was needed to build electronic circuits and the planar geometry of integrated circuits made a planar geometry for electronic circuits the natural choice.

As more electronic devices were being built as integrated circuits with transistors, boards were built on plywood workbenches using breadboarding. The top layer of the plywood sheet was replaced with a material called Bakelite, which has a standard thickness of 1/16’' or 1.57 mm. This labor-intense process was done manually and all components were wired using standoffs. Eventually, engineers started gluing sheets of copper foil on top of the sheet of Bakelite, allowing wires to be etched between components.

Integrated circuits additively manufactured on Nano Dimension's DragonFly LDM.

Advancements in plating and etching processes allowed full-scale production of PCBs with through-hole and/or SMD components by the 1980s and similar two-layer prototyping boards (protoboards) were available to accommodate these components. Sometimes called perfboards, these boards included pre-drilled holes in a regular grid with plated copper for soldering. Similar prototyping boards included copper pads on the surface layer, allowing prototyping with SMD components.

Today, designers have access to evaluation boards for specific components and microcontroller development boards. These prepackaged options can be used to create basic prototypes and experiment with different features but finished products are unlikely to resemble a prototype created from these boards. The adventurous designer can even etch their own boards, effectively mimicking traditional PCB manufacturing processes.

Traditional In-House PCB Prototyping Options

Additive manufacturing can decrease maintenance times for a range of aerospace components and supporting electronics.

Today, there are several traditional options for in-house PCB prototyping, each with benefits and drawbacks to consider.

Protoboards. Protoboards are still used for some less-complex circuits that run at lower speeds and frequencies. These simple, two-layer boards are normally used to mount through-hole components in plated holes on each surface of the board. The components can then be soldered to these plated holes. These boards can also be cut down to size with a hand tool and placed in an enclosure. While protoboards are fine for DC devices and low-speed (such as sub-MHz) devices, they suffer serious signal integrity problems at higher speeds. First, the lack of ground planes and printed traces causes circuits to have large loop inductance, leading to strong crosstalk and susceptibility to EMI at high frequencies. These prototypes will have little resemblance to a finished product and are best used to build a proof-of-concept.

Development Boards. Today, a micro-controller board like an Arduino is an excellent choice for in-house PCB prototyping for many applications, ranging from industrial or environmental embedded systems to IoT devices. Prototypes for applications that require more powerful computing capabilities might best be built on top of a Raspberry Pi or BeagleBone board, as these boards include the connectivity required to interface with other devices or a PCB. Development boards carry a low price tag and are reusable. They also allow a designer to focus on functionality rather than becoming mired in the finer points of PCB design; however, they don't allow a designer to integrate more components on top of the existing development board unless you purchase an add-on board or you build your own breakout board. Without an add-on board, you are limited to the functionality provided by the components you see on a development board.

Evaluation Boards. Many component manufacturers will release evaluation boards that are designed to mount to a specific component for a specific application. Some example components are high-speed FPGAs and high-frequency transceivers. Evaluation boards are very useful for interfacing with a small number of other components as part of the in-house PCB prototyping process. The useful aspect of an evaluation board is that the board is optimized to ensure signal integrity, allowing a designer to focus on designing functionality. Evaluation boards suffer the same drawbacks as development boards. Your functionality is limited to what you see on the board and you are unable to integrate additional features and functions without incorporating an additional board. With more advanced components, you risk introducing signal integrity problems when integrating additional boards, as evaluation boards are normally designed for measurement, rather than prototyping.

Manual Etching. Some designers are known to mimic etching in the traditional PCB manufacturing process using some common household chemicals. This starts with a CEM laminate that is covered with a copper foil. Regions of the board to be etched can then be traced within a handmade mask. Once the etchant is washed with a solvent (usually isopropyl alcohol), what remains is a functional two-layer board with copper traces and planes. Instead of a chemical etchant, a CNC mill can be used to cut away the copper foil, leaving behind traces and conductive planes on a two-layer board.

Tech Briefs Magazine

This article first appeared in the January, 2020 issue of Tech Briefs Magazine.

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