How to Prototype Your New Electronic Hardware Product

This article was originally published on Predictable Designs (a company that helps entrepreneurs and makers develop new electronic hardware products). Download their free cheat sheet 15 Steps to Develop Your New Electronic Hardware Product

Prototyping your product is all about learning. Each time you create a prototype version you will, or should, learn something new. Start with the most simple, low cost way to prototype your product. Then, with each prototype iteration you should progress closer and closer to a production-quality prototype.

During the early stages of prototyping it will be best to separate your product into different types of prototypes, each with its own goal. The most common strategy is to separate the appearance and feel of your product from the functionality. These are called looks-like prototypes and works-like prototypes.

NOTE: This is a very long article so here’s a free PDF version of it for easy reading.

Looks-Like Versus Works-Like

A looks-like prototype focuses on the look, feel, form, and aesthetics of the product. For your looks-like prototype you’ll use prototyping techniques such as foam, clay, 3D printing, CNC machining, and eventually injection molding (we’ll discuss all of these in detail shortly).

A works-like prototype on the other hand focuses on the functionality of the product. Its purpose is to ensure that any technical challenges have been resolved. For most electronic products appearance is mainly related to the enclosure and functionality is primarily related to the electronics.

So for an early, works-like prototype you may be using development kits such as the Arduino and Raspberry Pi along with techniques like breadboarding. This is called a Proof-of-Concept (POC) prototype and its aim is to demonstrate fundamental functionality of the product concept.

As soon as possible though you will need to migrate to the development of a custom PCB so it will be possible to merge functionality and form into a works-like-looks-like prototype.

Whether you start with a looks-like or a works-like prototype depends on your specific product and what aspect has the greatest number of questions and risk. If the look and feel of your product is especially critical then you’ll probably want to start with a looks-like prototype. On the other hand, if you are unsure of any technical aspects of your product then you may find it best to start with a works-like prototype.

If both aspects are equally critical then you will need to work on both separately, but simultaneously. For products without any big unknowns related to aesthetics or functionality, it’s better to jump right into creating a works-like-looks-like prototype.

If you decide to prototype each aspect of your product separately you have to merge them together eventually into a works-like-looks-like prototype. Your final prototyping goal is to achieve a production-quality prototype that will be identical to your final, mass manufactured product.

Prototyping the Electronics

How you begin prototyping your product’s electronics depends on what questions you are trying to answer. Every time you create a new prototype you should have well-defined questions that the prototype will answer.

If you have broad questions about whether your product will even work, or whether it will solve the intended problem, then you may be wise to begin with an early works-like prototype based on a development kit such as an Arduino or Raspberry Pi.

If there are no big questions about your product’s functionality then you should probably move right to designing a custom PCB. Most large companies developing products begin with a custom PCB. This is the fastest route to market, although not likely the cheapest.

Development Kit Prototypes (Arduino/Raspberry Pi)

Nearly all electronic products require either a microcontroller or a microprocessor. The Arduino series of development kits are based on microcontrollers. The Raspberry Pi and BeagleBone are based on microprocessors.

Microcontrollers and microprocessors are both fundamentally computer chips that run programs. Microcontrollers are less complex and less expensive, but also less powerful. Unless your product requires high-speed computer processing capabilities, you should go with a microcontroller. I would estimate that about 75% of the product ideas I see are best served with a microcontroller.

One advantage of a microcontroller that simplifies the electronics design is they are System-On-a-Chip (SoC) solutions. This means in addition to the Central Processing Unit (CPU), a microcontroller also includes memory (RAM and ROM) and other peripherals all embedded on a single chip. This greatly simplifies the required PCB design. Some microcontrollers are even available with more complex peripherals built-in such as a Bluetooth Low-Energy radio.

See this comparison table for a quick summary of the differences between a microcontroller and microprocessor.

Another key difference is that a microcontroller doesn’t require an operating system (Linux, Windows, Android, etc.) like a microprocessor. Programming a microprocessor based system with an OS is significantly more complicated than firmware development for a microcontroller.

Prototyping with a Custom Printed Circuit Board (PCB)

Eventually you’ll need to move beyond a development kit prototype to develop a production quality prototype. In my experience, it will be much easier to secure outside funding (co-founders and customers too) once you have a production quality prototype.

Development kit Proof-of-Concept (POC) prototypes are great for proving a fundamental concept but they are a long way from a prototype that can be mass manufactured. In fact, most larger tech companies don’t bother with a development kit prototype and instead they begin by focusing their efforts on creating a production-quality prototype.

Development kits are good at proving fundamental concepts but a long way from being manufacturable.Click To Tweet

This strategy usually speeds up development which allows the product to reach the market faster. However, this strategy tends to also increase the development costs since you won’t have learned things from your lower cost POC prototype. Starting with a POC prototype may reduce the number of revisions required on your production-quality prototype.

Prototyping a custom Printed Circuit Board (PCB) consists of two steps: producing the bare PCB, and soldering on all of the components. We’ll discuss the process for each separately.

Although there are techniques for producing your own PCBs at home, they are limited to simple designs. So you will most likely need to outsource your PCB prototype production.

Producing the PCB tends to be about 30% of the total cost to prototype the electronics. Roughly 60% of the total cost goes towards soldering on all of the components (assuming you don’t perform this step yourself). The remaining 10% is approximately the cost of the electronic components. These percentages are only very rough estimates since each design is unique.

For more information about the costs to develop, prototype, and manufacture a new hardware product see my article detailing all of these costs.

Fortunately, assuming you don’t make and assemble your own PCB boards, you’ll use the same process to produce your prototype boards and to manufacture your boards in high volume. This is not the case with the plastic enclosure for your product (more on this shortly).

Production of the PCB can be summarized by the following steps:

• The process begins with a laminate core made from woven glass epoxy. It serves as an insulator between conducting layers and it provides physical strength to the board.
• Single-sided boards consist of one laminate core with a copper layer on one side. Double-sided boards consist of a laminate core with copper layers on each side. Multiple layer boards consist of a stack-up of alternating copper layers with laminate core layers. Most boards will use 2, 4, 6 or perhaps 8 conducting layers.
• The layout design for each conducting copper layer is laser plotted on film and a light sensitive chemical “resist” is applied. The copper layers are then exposed to high intensity ultraviolet light which shines through the film. This light hardens the “resist” layer over any copper traces and pads.
• The copper layers are then processed through a chemical solution which removes any of the “resist” layer which wasn’t hardened by the ultraviolet light. This leaves hardened “resist” material only over the desired copper traces and pads. Another chemical is then used to remove any exposed copper not covered by “resist”. The hardened “resist” layer is then removed, leaving only the desired copper to form the traces and pads.
• A lamination process is next used to bond all of the layers together to form the stacked PCB.
• Holes are drilled through the PCB stack-up to form vias which are used to connect signals on different layers. Any holes for through hole components are also drilled. However, it’s generally best to only use Surface-Mount Technology (SMT) components to minimize your soldering costs.
• Copper is next deposited on all exposed metal surfaces including the inner walls of any holes. Additional copper is electroplated onto all exposed copper surfaces.
• Now that the bare PCB is complete the next step is to place and solder all of the electronic components. Robotic equipment called a pick-and-place machine uses a vacuum system to pick up the components and precisely place them on the PCB. Solder paste (a sticky mixture of solder and flux) is used to temporarily hold the parts in place.
• Finally, the boards are ran through a reflow oven which melts the solder paste to form a permanent electrical connection between the component and the PCB pads.

Prototyping the Enclosure/Case

Clay / Foam

Clay and foam are two of the simplest materials for creating early looks-like prototypes. Obviously these materials won’t make a functional prototype but they are excellent for experimenting with the form of your product.

Not sure of the best size or shape for your product? Then definitely begin by experimenting with clay and foam. You can purchase all of the necessary equipment and materials at any hobby or craft store.

Remember to always start with the cheapest, simplest types of prototyping to gather as much information as possible. It’s much easier, and way cheaper, to iterate your product in clay or foam rather than using more complex prototyping technologies like 3D printing.

3D Printing

3D printing is an additive prototyping process that adds material to create the desired shape. The term 3D printing is a broadly used term that actually refers to various prototyping technologies.

Let’s look at the three types of 3D printers in more depth:

Fused Deposition Modeling (FDM) — This is the most affordable method of 3D printing and is therefore the most common technology used for home 3D printers. This technology can produce prototypes with a moderate amount of detail.

FDM printers work by feeding plastic through a heated nozzle. The material is melted and deposited layer by layer, with each layer fusing to the layer below it. FDM printers are limited in the fine details they can produce so an SLA printer is a better option for complex prototypes.

Stereolithography (SLA) — SLA is a more costly process which is used mainly on high-end, home 3D printers and by professional prototype shops. This type of 3D printer works by curing resin with light. The light hardens the liquid resin layer by layer in a process called photopolymerization. SLA is a very accurate method of 3D printing that can make parts with many fine details.

SLA printers also produce a much stronger prototype because the layers are chemically bonded together. Prototypes produced by an SLA printer tend to look more professional than ones created with FDM printers.

A good strategy for many entrepreneurs is to purchase a low-cost, FDM based, 3D printer for producing early prototypes. Once the appearance and strength of the 3D printed prototype become more important you can move to using a professional prototype shop with SLA printers. This strategy will save you money and speed up development for many products.

Selective Laser Sintering (SLS) — An SLS system uses a laser to sinter (i.e. harden) powder materials layer by layer to form the desired shape. A big advantage of SLS is it can be used to create metal prototypes. SLS is too complex for home 3D printers so it’s only an option when using a professional prototype company.

CNC (Computer Numerical Control) Machining

The opposite of an additive process is a subtractive process. As the name implies a subtractive process removes material to form the desired shape. The process starts with a solid block of plastic or metal. Material is then carved away to form the final sculpted prototype.

One of the primary advantages of CNC machining compared to 3D printing is that you have much more flexibility in regards to the material used. Not only can you create prototypes from plastic or metal, but you can select very specific plastic resins which precisely match the material you will use for mass production.

Injection Molding

3D printing is fantastic at producing tens of parts. However, it’s not practical for producing hundreds or thousands of parts. Ultimately, injection molding will be necessary to replicate your product’s enclosure in higher quantities.

Not surprisingly, the injection molding process starts with the creation of a mold. Molds are machined from metal, and the hardness of the metal determines the mold’s lifetime and cost. For prototyping, or early production, aluminum molds are generally the best choice. Aluminum molds typically cost a couple thousand dollars each and can produce up to about 10,000 parts.

The mold forms two halves that are held together as hot, molten plastic is injected at high-pressure into the mold. The high-pressure is necessary in order to produce fine details in the part. Once the plastic cools and solidifies, the mold is opened and the part is removed.

Most designs will require significant modifications in order to prepare them for injection molding. Whereas 3D printing can reproduce just about any shape you can imagine, injection molding has strict design rules that must be followed.

Be sure whoever designs your enclosure understands injection molding, otherwise you are likely to end up with a product that can be prototyped but not manufactured in high volume.

Reaching the point of having a fully functional, works-like, looks-like prototype is a huge accomplishment. So pat yourself on the back once you achieve this milestone! But don’t get too excited just yet. The transition from prototype to mass manufacturing is one of the most underestimated steps to bringing a new hardware product to market. So, I’ll be covering that topic in a future article.

Originally published at predictabledesigns.com on July 24, 2017.