In the last section, you learned all about how to create the design files that will bring your project from just a figment of your imagination all the way to a working prototype and then into a design that is ready to be manufactured.  In this section, I will give you an overview of the process to take those design files to market.

 

Step 6: Manufacturing Prototypes to Production

If you have made it this far, you have a design file that represents the PCB artwork to be laid out in copper.  This is where a real board is finally created from all of your careful planning and months of researching, breadboarding, and designing.  You have many options to turn that artwork into a real, physical board and then assemble that board with real components. 

 

Manufacturing Terminology

• Solder – Metal that has a low melting point and used to attach components to the board. Some solders contain lead, which are not allowed in Europe.  Lead-free solders are known by the standard RoHS.
• Flux – A chemical included in most solders to help the solder flow freely when it melts. Also available as a liquid, which is very toxic.
• Solderpaste – Tiny balls of solder suspended in solder flux. This is spread onto the board to allow soldering of SMT components
• Stencil – A metal sheet that is cut by laser and used to place solderpaste on the board at specific pad locations.
• Soldermask – The area of the board that is not to receive solderpaste. This is the file that creates the stencil.
• SMT – Stands for Surface Mount Tech, which means that components are attached via solderpaste and then baked in an oven.
• Solder Profile – The oven temperature ramp, soak, and cool down procedure over time, as specified by the component’s data sheets.
• FR4 – The most common type of board material, which is stiff and uses a fiberglass dielectric.
• Semi-rigid – A more flexible board than FR4.
• Flex – A more flexible board than semi-rigid.
• Dielectric – The material that insulates traces and planes from touching one another.
• ICT – In-Circuit Test, which requires test points built into your board and a pricy test fixture that looks like a bed of nails. The test checks for properly assembled boards.
• Flying Probe Test – A manufacturing test that covers some of the same checks as ICT but without built-in test points or test fixtures, and with less test coverage.

Manufacturing Options By Phase

The first PCB’s that you bring up will not be perfect.  You will not go straight to production.  Despite all of your hard work in schematic and layout, you will fail to connect everything perfectly.  It is highly recommended to build just a few boards in the first batch and then bring up just those few to ensure that the artwork is correct before ordering thousands upon thousands more.  Then, a pilot build will help hone your process for the onslaught of thousands or even millions of boards.  Do you want to find out that your process is broken after you have developed 100 boards or one million boards?

 

Manufacturing Phase	PCB Manufacture Options	Assembly Options
Prototyping	·       DIY laser printer & etching ·       Circuit Printers ·       Quick-turn board shop	·       DIY Toaster oven and hand-soldering ·       Prototype assembler
Pilot	·       Quick-turn board shop	·       Prototype assembler
Volume	·       Domestic vs. foreign board shops	·       Domestic vs. foreign assemblers ·       Self-purchase parts, distributor, or assembler purchase

 

Prototyping Manufacturing Phase – DIY Options

The very first time you build a PCB for a new design, the quickest and cheapest way to get it done in very low volumes is to simply do the work yourself.  There is some upfront investment in tools that has to be made, but you can continue to use those tools for future projects.  There is also a real risk that you will do things improperly and create your own headaches.  It depends on how willing you are to learn a new skill and take a risk that you could end up wasting your time and effort.

 

Old-School Board Etching

In order to build the PCB yourself, you have some options.  The old-school way to build your own board was to purchase copper-clad circuit board blanks, lay plastic traces on the board, and then etch away the exposed copper using a powerful and toxic etching solution.  This method is fine as long as you have large pin pitch components.  It won’t work for today’s modern 1/2 mm pitch components. 

 

Hand-drawn circuits with marker and etching kit

 

Laser Printer Board Etching

To reach a finer degree of precision, a laser printer can be used to print the Gerber artwork from a CAD program on special transfer paper, available from PulsarFX as a PCB Fab-in-a-Box kit.  A laser printer’s toner is essentially powered plastic that is fused to the paper.  By fusing the toner to transfer paper, the idea is that you can reheat the toner and it will release from the transfer paper onto your blank copper circuit board, which is part of the kit.  You will need a high-temperature laminator, and it can be tricky to find one that works just right.  In my experience with this method, it was a little spotty.  Thankfully, you can trace over any incomplete traces with an ordinary marker pen, and that will help resist the etching compound from removing the copper at the gaps in the traces.  However, you lose some of the precision that was gained by the laser printer process.  In order to create a multilayer board, you must print out each layer and etch it separately, and then glue the layers together.  Then, you have to drill through any of your through-holes or vias and make a connection between the layers with solder.  With enough practice and experimentation, this method can be successful.

 

Laster printed etch resist and final product with SMT LEDs

 

Direct Circuit Printer

A recent invention in circuit board prototyping is the circuit printer.  There are many exciting developments in this area that will surely produce useful tools for your prototyping work in the near future.  Some notables to check out are: Cartesion Co’s Argentum and the soon-to-be-produced 3D circuit printer from Voltera.  The big concern that I have for these devices in the near term are with fine pitch devices.

 

Argenutm and Voltera Circuit Printers

 

Quick-turn PCB Services

The best choice for many makers even with these available DIY choices is to simply order a quick-turn board from a board shop.  They can be found with very reasonable prices and ship the boards in a few days.  You can still assemble the board yourself, which is where you will get more value.

 

Ordering Parts

However you acquire your PCB, the next step in the DIY process is to assemble the board.  Before you can do that, you have to source the parts.  This is a time-consuming activity.  It is nice if you can find all of your parts from a single vendor, but often you will have to order from several and coordinate shipping so that you aren’t waiting on a single part to start your build.  You can’t start meaningful assembly until all of the parts arrive. 

 

When ordering parts, be prepared to make decisions that you never had any idea that you would need to make.  You may know the exact major electronic components you will be ordering, but there are a collection of supporting components that need to surround those major components.  You will find that there are many more types of resistors, capacitors, crystals and other miscellaneous parts that have a million variants. You have to specify things like brand, package, size, value, tolerance, material, lead or no-lead, temperature, wattage, operating voltage, etc., when all you want is a 1µF capacitor!

Your parts arrive packaged in little antistatic baggies or boxes.  Now you have to match up each one of those components to a refdes on the schematics and formulate a plan.  I line all my baggies up in a shoe box in the order that I will apply them to the board and prepare notes for myself so that when the assembly starts, I don’t forget what I am doing.

 

If you are planning to have your boards assembled by an outside company, you can save money by ordering the parts yourself.  Assemblers will charge a markup on any of the parts they order on your behalf.  Just be sure to ask your assembler what kinds of machines they will use so that you get the right kind of packaging.  An automated “tape and reel” machine requires that your parts are delivered in that fashion.  If you don’t order a full reel of parts, can your assembler accept “cut tape” parts that have been cut off of a reel?

 

Parts ready for assembly

 

SMT Board Assembly

You can assemble your SMT board yourself with the help of a toaster oven and solderpaste.   If you had your PCB developed by a board shop, you have the option to order a stencil for the solderpaste.  They are laser cut, and you can use this to spread solderpaste across the board, laying it down only on the areas where a component pin will land on a pad.  You can get by without a stencil, but there is a higher chance of solder bridges, which are bits of solder that connect adjacent pads.  Solderpaste needs to be kept refrigerated, and you only have an hour or so before the solderpaste becomes a liquid, although it depends on the temperature of the room.  I have extended it to a few hours with no issues.  The hardest part of placing components by hand is to get them to land on the solderpaste cleanly, and then not bumping them when you are placing nearby components.

 

Solderpaste on a board and then the parts are placed and baked

 

Oven Baking

Commercial SMT ovens bake the boards using a precise temperature profile to ensure that all of the solder melts and you don’t cook your components too long.  You can purchase a home SMT oven for a few hundred dollars, which includes the temperature profile.  It’s all automatic, which is great.  I have only used a regular toaster oven from a household store.  The directions that I found online were to simply insert the board in the oven, crank the temperature to 400 degrees, then watch for the solder to melt.  The grey solderpaste becomes shiny silver when it melts.  You can watch this process happen through the window of the toaster oven, as the temperature washes over the board, in my case from the corners inward.  Once all of the solder turns silver, you wait about 15 seconds more and then remove the board from the oven.  There is risk with this method of some cold solder joints, and you will have to touch up any solder bridges you find with flux and a fine-tipped soldering iron.  Use a 10x microscope if you can find one, and look for issues.  Take your time.  It is better to find the problem now than when you power up or your board or debugging a software issue.  Use a multimeter to check for shorts between power and ground and between traces that are hidden.  I have been able to get several good boards out of this process in the first and only time that I tried it.  Your mileage may vary.

 

Prototype/Pilot Manufacturing Phase – Outsource Vendor Option

The low-volume board development process is not cheap nor fast.  If you want it fast, prepare to spend a lot more.  Quick-turn PCB builds can be done for a premium in 24 hours, if you are on a tight schedule.  Things get a lot more affordable as you approach a 5-day turn, and become most affordable at a 2-week turn.  You will have to quote the boards in many different volumes because you may be surprised to find that building 100 boards isn’t ten times as expensive as building 10 boards.  It can be just twice as expensive, for example, and may be worth it to get as many prototype boards as you need for your testing purposes.

 

When you receive your prototype boards, the first thing to do is a visual examination to look for copper traces that may be touching where they are not supposed to be touching.   You will need to refer to Gerber files and layout to compare the real PCB to the design files.  Measure a few points with a micrometer.  Once the board passes visual checks, you can probe the board with a Volt Ohm Meter (VOM) and ensure that there is no short circuit between the power and ground pins of any device.  This is heartbreaking if you find it, because it can be hard to trace back where the error occurs.  All vias pass through any internal power and ground planes, and if there was not sufficient anti-pad clearance inside those layers around all vias, you could get a power and ground short.  You will need to then check every signal versus power/ground to find the offending signal.   If you pass that check, you can then measure to ensure that all signal traces don’t short against power or ground.  If you find that all of the boards check out, move on to the assembly step.

 

The assembly of your electronic components onto a low volume of prototype boards can be very expensive if completed by a prototype assembler vendor.  Be prepared for some pricey quotes!  To make matters worse, the prototype assemblers are not in control of the schedule.  They have large repeat customers that will knock your product to the back burner no matter what they may have quoted you regarding turn times.  A fast turn time for the assemblers is five days.  It takes time for the assembler to examine the BOM, order the parts, receive the parts, configure the tape-and-reel machines (if used for your volume order), find pin #1 on all devices in your silkscreen and layout files, and then do hand soldering touch ups after your boards have been run through the automated assembly process.

You may not have a test procedure for the prototype builds, but it would be helpful to define manufacturing tests by the time the pilot builds occur.  The pilot builds are meant to test your process against a larger volume of manufacturing that will follow.

 

Volume Production Manufacturing Phase

When moving from pilot builds to manufacturing builds, you biggest concern will be cost.  You certainly don’t want to pay the pilot build prices or you will go broke.   You must choose between domestic and foreign assemblers and board shops, keeping in mind the tradeoffs between cost, language barriers, shipping charges, and travel abroad to fix issues.  Some assembly shops have domestic pilot lines with foreign volume lines, and those can be a good choice because their teams already work together.  This phase is more about business strategy than engineering, and approaches will vary greatly between developers.

 

That’s the big picture overview of what lies ahead if you plan to bring your own gadget to market. 

 

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