Before You Order a PCBA Prototype: Everything You Need to Know

Seeing your PCB design become a physical assembly for the first time is an exciting milestone. After hours of designing, reviewing and refining your circuit, it's finally time to find out whether everything works as intended.

It's also the stage where many engineers start asking the same question:

"What if it doesn't work?"

The good news is that's exactly what the prototype stage is for. Very few products go from first prototype to full production without changes, and that's perfectly normal. Whether you're building your first PCB assembly or you've developed products for years, understanding the prototyping process can save both time and money.

In this guide, we'll explain everything you need to know before ordering a PCBA prototype, from preparing your design files and requesting quotations to understanding costs and choosing the right Contract Electronics Manufacturer (CEM).

What information do you need before requesting a quotation?

There are several pieces of information you will need to give to your electronics manufacturer. It is best to ensure this is all correct prior to sending out an Request for Quote (RFQ) to ensure a quick and accurate quoting process.

• Bill of Materials (also known as the ‘BOM’) – A BOM is essentially the recipe for the product, most customers prefer to create this in a spreadsheet but if it is clear then you can use whatever programme you like. On the BOM, you will want to list the most important information regarding the build, as this will be used for two things; the purchasing and the manufacturing. You want to ensure it has information such as component type, component value, component size, component tolerance, reference designator and any other information that will help the manufacturer build your product correctly.

• Pick & Place data – This data is what tells the pick and place machines where each component goes on the PCB. Ideally you will want to include the following: X & Y coordinates, rotation, component code, component type. This data is usually given in an excel spreadsheet so the manufacturer can upload directly to their machine. If you are unable to obtain this data then do not worry, most machines can be set up manually, however the increase in set up time can result in an increase in cost.

• PCB Gerber Files – Gerber files are digital files used to manufacture printed circuit boards. The data shows the PCB manufacturer what the PCB should look like, and they use this to tell the machines in the factory how to build each physical layer. Gerber files will contain copper layers, solder mask, silkscreen, hole sizes and any other relevant features on the PCB.

• Assembly Drawing - If your PCB contains unusual components, polarity requirements or specific assembly notes, an assembly drawing helps ensure everything is built correctly.

• Final Manufacturing Details – During the prototype stage you might not be fussed about some of the details such as ident/silkscreen and solder mask colour, but it is still important to reference this to your supplier. PCB manufacturers will also panelise your PCBs onto production panels to maximise manufacturing efficiency. If you have specific panellisation requirements, be sure to discuss them before production begins.

All of this information is essential to get right prior to sending an RFQ to your chosen manufacturer. If you spend more time preparing these things there will be fewer questions, making the quotation process easier for both you and your manufacturer. This part of the process is where we commonly see delays in prototype builds, we recommend you also read our previous blog post ‘7 Common Reasons PCBA Prototype Builds Get Delayed (And How to Avoid Them)’.

Choosing the right CEM

Now you have everything you need it is time to send all of this information off to a CEM (Contract Electronics Manufacturer). You might search Google and get overwhelmed by the results and you might just click on the first company that comes up but that isn’t the best strategy. There are lots of CEMs around the globe, you should choose a CEM who is the right fit for your product and your company. A few questions you should be asking when exploring options are:

• Does this CEM align with our company values?

• Does this CEM offer prototype work (some will specifically focus on full scale production)

• Can they match our product specifications, and do they have the required capabilities?

• Do they meet our requirements for quality? (E.g. ISO 9001, AS9100)

• Do we have any other requirements that the CEM needs to meet? (E.g. IATF 16949, NADCAP)

• Are their technicians IPC trained?

• Where are their manufacturing facilities located?

• Can they source obsolete or long lead-time components? (If required.)

It is worth asking yourself these questions prior to approaching a CEM and only approaching relevant companies and to not assume every CEM has the same capabilities.

What costs are involved?

• PCB tooling costs – PCB tooling preparation is an important part of the manufacturing process. During this stage, your Gerber files are reviewed by an engineer, who panellises the design (arranging it efficiently onto manufacturing panels) the data to manufacture the PCBs as efficiently as possible. This process also ensures the data is correctly outputted so the machines can read the data and there are no complications during manufacture. 

• Stencil – During the assembly process a stencil is required to print the solder paste directly onto the PCB prior to placing the components. The stencil is made bespoke to your PCB design, and one stencil may be required for each populated side of the PCB.

• Materials – This includes the bare PCB and all electronic components such as resistors, capacitors, LEDs and connectors.

• Labour costs – Labour for both PCB manufacture and PCB assembly. This will include time to set up the machines; the actual time spent on manufacturing and machine changeover and programming time.

• Additional requirements – Sometimes you might have additional requirements such as conformal coating, an AS9102 FAIR or specific IPC testing (micro-sections, pull tests). It is important to remember these will all incur additional costs through the PCB manufacturer or the CEM.

Why are PCBA prototypes expensive?

The first prototype is often the most expensive version you'll build. But don’t let this scare you for future production orders, there are a few reasons why prototypes can be more expensive.

• Tooling costs – You will only incur these costs once on new products to that manufacturer.

• Stencils – Stencils can be a large cost however once your PCB design has been tested, changes made if necessary then you will only need to purchase your stencil once and these can last for thousands of prints.

• Minimum order quantities (MOQs) – Many component suppliers will have MOQs which makes things difficult and expensive when you are getting 1 prototype made and you have to order 50 of one part. The initial outlay will be expensive however the unit costs going forward will be much cheaper.

• Material Costs – PCB manufacturers often have a minimum production panel size. Even if your PCB only occupies a small area of that panel, you'll still be charged for the full panel, making low-volume prototypes more expensive per unit. 

• Additional Costs – If you require an AS9102 FAIR, IPC testing etc. usually this requirement is for the first order only to confirm the part is manufactured correctly.

Although these costs may seem daunting, many are one-off expenses that won't apply to future production runs.

The prototype stage is important as it highlights to you and your team what works and what doesn’t, but this also means making design changes and remanufacturing PCBAs with all the above costs. At Advanced Assembly Solutions we encourage our customers to design their prototypes with this in mind.

Is there a way to keep costs down without compromising on the quality?

Yes, there is! You don’t always need to create multiple revisions of the same PCB which is costly. Instead, we can make changes to the same board by changing components, cutting PCB tracks and adding wire links where required. We pride ourselves on being flexible and allowing the customer to make changes during or after production. This method is quicker and more cost-effective. Once you're happy with the design, you can update the PCB layout and remanufacture the board incorporating those changes.

We also recommend that you read our blog post on how to reduce PCBA prototype costs here, this goes more in-depth about other ways to reduce costs.

RoHS compliance

Every person working in the electronics industry should be aware of RoHS.

When designing PCBs and selecting your components this is something to be aware of. If you are building a product that is lead-free, then the majority of components will be safe. However older components and technologies mainly prior to 2006 contained lead so this is something to be aware of.

Whether you're building your first proof of concept or refining an existing design, having the right CEM can make the prototype stage faster, less stressful and ultimately more successful. If you'd like to discuss your project or get advice before requesting a quotation, we'd be happy to help.