When it comes to prototype printed circuit boards, they have a particular (and vital) purpose. When we’re making PCBs, we need prototypes to see if our concepts and designs actually work. Prototypes are also an ideal way of working out all the kinks in the design or testing out several PCB designs.
In other words, if something isn’t working or is misaligned or incompatible with the rest of the design, the prototype will show it.
Why We Need a PCB Prototype
The main reasoning behind a PCB prototype is — in a nutshell — cost-effectiveness. High-quality PCB fabrication is a tedious process. It takes time, effort, and resources to manufacture a series of PCBs. Now imagine doing all of that and making a 500-piece series only to realize that something isn’t working.
So prototypes are meant to test the functionality of PCBs. They can either be rudimentary, basic versions of the final design or fully-functional ones. The PCB manufacturer and the engineers decide which option to go for (based on the potential applications, overall design, and intended functionality of the PCB).
Aside from this, prototypes are also a great way to test a few PCB designs and decide which one to go for.
Before You Jump Into Prototyping
Building a PCB prototype is a 20-step process. So it isn’t something you want to get into unless it’s absolutely necessary.
Before you get to the actual prototype building, make sure that you:
- really need the prototype
- are prepared for the entire process
If you have a brand new design or an old design that you’ve made significant changes to, you probably do need a prototype. However, if you already have a functional design that you know works, then prototyping might be a waste of time and effort.
If you decide that prototyping is the way to go, MKTPCB offers a prototype service with a short turnaround time and fixed delivery date. That way, our clients can figure out the kinks in their designs before the boards are manufactured and get definitive results within two to seven working days.
So what happens after you realize you need a prototype? Well, you need to think about the prototyping process and make some decisions. For example, do you want a multi-layer board, or will one layer be enough? How thick and big do you want your board to be? Consequently, what’s the copper layer thickness and trace spacing you’re going for?
Aside from that, you also need to think about:
- hole size
- annular ring
- surface finish
- solder masks (and their colors)
Building a PCB Prototype in 20 ‘Simple’ Steps
Once you’ve made all the necessary decisions and communicated them to the PCB manufacturer, you can get to the building of a PCB prototype.
Step #1 — The Design
There is various design software that will allow you to design a perfect PCB that fits your needs.
Step #2 — More Designing (Or the Schematics Design)
First, you need to determine the board’s functionality. What will you use it for? What are the necessary characteristics of the board, and how does that relate to component placement?
The schematic design has that and all other necessary information that engineers need to actually make the prototype (such as the board’s grid, for example, as well as the size).
Every new step in the designing process requires a functionality test. If we do this, then any defect will be noticed instantly and can be sorted out sooner rather than later, which improves the overall cost-effectiveness of the entire process.
Step #3 — BOM
BOM or bill of materials is a list of all products, materials, and add-ons that we’ll need for the prototyping (and manufacturing) process. This is a vital step, especially if you aren’t getting the parts yourself but outsourcing that task to a manufacturer.
BOM should include information about every component, including how many we need, their codes and manufacturer part numbers, specifications, such as units, and of course, their individual location on the board.
Step #4 — Even More Designing (Or the Routing Design)
The next step is to determine the trace routing. We have to specify the way and layout of all traces and how they connect the components.
Step #5 — The Last of Design Checks
As mentioned, we need to regularly and routinely perform functionality checks. That’s the only way to iron out all design flaws and make sure the prototype (and consequently, the final board) will work properly.
Performing one final check before we move from the designing to the fabrication phase is vital. Otherwise, the fabrication process will turn into a lengthy back-and-forth nightmare.
During this final check, we should check for heat spots and do several specific checks:
- check up on the design rule
- do an LVS (layout-versus-schematic) check
- check up on the electrical rule check (ERC)
- and do an antenna check
Step #6 — The Photo Film Stage
In this step, the manufacturer will create a photo film based on the entire design you’ve done so far. The photo film is actually a thin layer of plastic that has clearly marked conductive and non-conductive parts of the beard.
Step #7 — Time to Print (Those Inner Layers)
Once we have the photo film, we should move on to applying and pre-bonding the copper layer(s) to the substrate material. This process is somewhat complicated because it involves applying a photosensitive film to the substrate (onto which we already pre-bonded the copper) and exposing that film to UV light.
The UV light hardens the photoresist layer, which (in its hardened state) protects the copper layer. When we remove it, it will leave the copper exactly where the design specified it should be.
Step #8 — Aligning the Layers
This step is quite simple. If we have a multilayer board, we need to align all the layers. We should do this with great care because there’s no room for error. Once aligned, the layers can’t be fixed. We also need to be careful about punching in registration codes.
Step #9 — Fusing the Layers
Next comes the step that results in an actual PCB. After we aligned the layers, we have a prepreg. However, we need to fuse the layers in order to have an actual PCB.
First, we need to stack all the layers in an exact order — prepreg goes into an alignment basin, then we put the substrate layer, followed by the copper sheet, then a bit more prepreg, an aluminum foil, and finally, the copper press plate — onto a steel table.
After we layer up our board, we need to bond the layers with a bonding press computer. It will heat our layered stack and apply the necessary pressure to it, so the layers bond together and then cool everything off.
Step #10 — Time for Some Drilling
The next step is extremely precise drilling of 100-micron holes where the components will go.
Step #11 — Copper Plating
Finally, it’s time for the copper plating. This first layer of copper comes in the form of a chemical bath and covers the entire board (including the holes we just drilled).
Step #12 — Time to Deal With the Outer Layers
Essentially, we are now repeating step #7 and applying another layer of photoresist. That will create imaging on the outer layer.
Step #13 — Another Layer of Copper (and Tin)
Now that we have outer imaging, we can apply another copper layer that we will only deposit on the board’s parts where we actually need it. Next follows a thin layer of tin that protects the copper during the next step (which is final etching).
Step #14 — Now Comes the Etching
The prototype board is then treated with chemical solutions that remove excess copper. Thanks to the tin layer, the copper will remain in those areas where we need it as a conduit.
Steps #15, #16, and #17 — Solder Mask, Surface Finish, and Silkscreening
Next, the board is thoroughly cleaned, and a solder mask is applied. After that, we add another layer of plating (more often than not, it will be a gold or silver finish). Finally, we apply a silkscreen that holds all the necessary information about the board and all the components.
Step #18 — Cutting
Next, we need to cut the board from the bigger panel we made it on.
Steps #19 — Sourcing the Components
Remember that BOM? Here’s where it comes in handy (or better said, necessary). Now that we have the board, we need to source the components. If you choose a manufacturer such as MKTPCB to source your components, all you have to worry about is the BOM. Otherwise, you’d have to find suppliers and order all components yourself.
Step #20 — Assembly
The final assembly of the board includes several steps:
- first, we attach the components
- we apply the solder paste to the board
- we use a special machine to place the components on the surface
- we solidify the solder paste via a reflow oven
- because there can be some movement during the reflow, at this point, we need to do an assessment and check if everything is in order
- then, we insert the components that go through the through holes
- and finally, we conduct a functionality test
A Few Parting Words
Although not a simple one, building a PCB prototype is often a necessary process. The 20 steps we went over are something that MKTPCB staff knows by heart as our prototype service has been and continues to be in high demand.
While building a PCB prototype, there are a few things to keep in mind:
- Component-to-component relations — be careful while determining the minimal tracing between the components as it can affect the soldering process.
- Component-to-edge relations — if there are too many components too close to the PCB edge, there might be some issues with the assembly. Make sure to space them away from the edge.
- Component locations — to avoid any shadowing of small parts by the larger ones, we need to think about each component’s location. The soldering process might get complicated if we don’t.