With the market becoming more and more competitive in every segment, time-to-market is emerging as the most important factor defining a product’s success. However,
Designing and prototyping a product takes a long time, not because of the complexity involved, but because of the lead times associated with the outsourced production of each part. Most of the outsourced processes are sequential in nature, so the overall lead time for prototyping becomes the sum of individual lead times for each process.
For a new product, the first thing done is mechanical design freeze. All other components, such as assembled PCB boards, are designed to fit into the decided mechanical design. So everything has to wait until the mechanical design and prototyping is complete. Mechanical designs also get revised later, if other parts have some constraints.
Once the mechanics is done, PCB designs are finalized and their gerber files are sent to the PCB manufacturer. These files have to be revised sometimes to suit capabilities of the manufacturer. For more advance PCBs, with track width below 4mil, you may have to get the work done abroad. As the manufactured PCBs are sent to you via courier, you should include this transportation time also in your time schedule.
The PCBs and the components to be mounted on them are then sent to an EMS (electronics manufacturing service). Fortunately, components procurement doesn’t have to be sequential; you can do it in parallel with production of the PCBs or earlier. Some EMS can even procure the components themselves, but they are reluctant for low quantities. So you may have to procure them yourself.
If a PCB board has SMD components, the EMS will have to make the stencils for automatic placement of the components through chip shooters. But you can ask them to do it manually, if the quantities are small. Again, the work will be done depending on the availability of resources and the process can take weeks.
We have not included the negotiation time taken with all these vendors after the receipt of their quotes.
When the boards are ready, fitment in the mechanics is checked and then the boards are tested for functionality and compliance. If there happens to be some flaw in design or non-compliance with the standards and specs, the whole process will have to be repeated.
Some manufacturers provide turnkey solutions, where they make the PCBs, source the components, make stencils and assemble PCBs, all at one place. Though this saves some time, the processes usually need to be much faster to meet the pace of the market. Some of the key issues involved in producing the prototypes are:
Low quantities, low priority. For prototyping you would only be producing a small batch of, say, ten pieces. If you see the business angle, it will not interest most vendors, or the work will be done at a much higher cost, which can hit your project’s budget. The components you buy from online stores will come at very high prices, and your work at EMS will be done on low priority due to their small quantity.
Tooling cost for all parts. For producing the PCBs and assembling them at EMS, you need to pay an additional one-time cost, which is called tooling or setup cost, for every project. And if the design gets revised after first prototyping, which is normally the case, you will have to pay the tooling cost again. Also, if there is a change in PCB design, new stencils will have to be made and the money spent on previous stencils will go waste.
Time delay. As already mentioned, a lot of time is wasted usually in cost negotiations, transportation, sequential nature of processes and delays caused at EMS due to lesser quantities, other than the processes themselves.
With the recent availability of desktop manufacturing equipments, such as SMD pick-and-place machines, ovens, PCB-prototyping machines, stencil printers and 3D printers, all the above-mentioned prototyping work can now be done in-house and a lot of time and money can be saved. These equipments are expensive but, in the long run, can save you money and, most importantly, the time to market. Let us have a look at these equipments one by one.
Using 3D printers, which got introduced commercially only recently, you can produce almost any part. These printers can be used for checking the mechanical design and fitment. In regular process, you get the designs made and then send them to the manufacturer. Then there is a long wait before you receive the prototype to check everything and finalise the mechanics. With a 3D printer you can immediately fabricate your design and check it. It accepts .stl files and converts them to gcode files to print all layers one by one. Fig. 1 shows a 3D printer.
The material of the printed prototype will off course be different, but you only want to check the dimensions, fitment and integration of different parts. Sometimes your prototype could have dimensions larger than what your 3D printer can handle. In that case you can scale down the dimensions of each part and check the fitment and integration in this scaled down dummy.
3D printers also come in the form of DIY kits, such as Prusa Mandel i2. You get all the parts of the printer but you need to follow its manual to assemble it and install everything before you can produce anything. These printers are normally less precise and you have to do a lot of calibration before starting work on them. But such printers are usually cheaper and can be good for basic mechanical models’ dummy checking. Table I lists some manufacturers of the DIY-type 3D printers.
But if you are looking for more precise and reliable prototyping, you should go for ready-to-use 3D printers. These printers come assembled with reliable mechanical structure and give precise results as per specs mentioned by their manufacturers. Most of all, nil or very little calibration is required in such printers. Table II shows some assembled desktop 3D printers from different manufacturers.
Here are some more pointers to help you select the most suitable 3D printer for you:
Print platform. This is the maximum dimension that a printer can print. Select appropriate dimensions for your requirement. If the prototype is larger than that, either print a scaled down version or break it into parts that can later be combined.
Resolution. Check for horizontal and vertical resolutions in the specs sheet. The vertical resolution will define the thickness of each layer. Better resolution prints smoother surfaces. Similarly, horizontal resolution defines how fine the extruder can move in XY plane. The printer with finer XY resolution can print finer features in the model.
Print speed. This will give you an idea about how fast your designs can be printed. It is normally defined as the time it takes to print a specific distance in the Z-axis.
Number of extruders. Extruders are the print heads. The number of extruders is generally associated with the number colours that the printer can handle at a time.
SD card and display support. Some printers have an interactive display to help select all the functions, but this comes at an additional cost. SD card support is also an important feature; the design can be copied in the SD card and the printer keeps printing without the need of an attached computer.
Desktop PCB prototyping
With the mechanical design verified, the next step is to make your PCB design such that it fits into the mechanics. Once the design is done using PCB design software, within the dimensional constraints set by the mechanics, you will have to get some of these PCBs made so that you can mount all the components and test the boards for functionality.
Since most manufacturers are not interested in low quantities, it is best to make these PCBs in-house. Though some people use photo-resist and UV systems for making a few pieces, these techniques are inaccurate and time consuming. Besides, making double-layer PCBs with such techniques is very cumbersome.
Various desktop PCB-prototyping systems available these days help in making the PCB prototypes very quickly (refer Fig. 2). These systems are majorly of two types: mechanical and laser milling systems. Both types of systems create conductive paths and pads by milling insulating paths. The insulating paths separate the electro-conductive copper surfaces that form the network of conductive paths.
A mechanical milling system contains a rotating drill head that works on the copper-clad sheet, milling all insulating paths. It is comparatively slower than a laser system which uses an energy-emission device to focus a highly concentrated stream of photons onto a small area of a work-piece for milling the insulating paths. Table III shows some mechanical and laser-type PCB-prototyping systems from different manufacturers.
Next, all the required holes need to be drilled. Both these systems can drill holes for mounting through-hole components. The specifications of these systems are simple and easy to understand. You can look at specs, such as working area, resolution, speed, drill sizes and power consumption, to decide a suitable system for you.
SMT pick and place
Once the PCBs are ready, you need to mount all the components and test the boards. Mounting of through-hole components is easy but SMD components require some skill and patience. So most people avoid doing it themselves and outsource the job, which costs money for making stencils and tooling, and time delay is always there.
With desktop SMT machines the SMD boards can be assembled in-house. Fig. 3 shows a desktop SMT pick-and-place machine. Such machines come in completely automatic and semi-automatic forms.
In an automatic system, no operator intervention is required. The system automatically applies solder paste on the pad and then places the components on corresponding solder beds. The placement is not very accurate in most cases, but during reflow oven stage the parts tend to organise nicely.
In a manual system, the operator controls the application of solder paste and placement of parts. The placement can be much more accurate in this case. But you may not want an operator, who could make errors. Besides, the process will be much slower than with an automatic machine.
Some manufacturers have also come up with solutions that include PCB milling, solder-paste application and pick and place, all in one system. Do check the specs of all the three systems separately to see if they suit your requirements. Table IV shows some desktop pick-and-place machines from different manufacturers.
Reflow ovens and wave-soldering machines
The solder paste is applied and components are placed on the solder beds by the pick-and-place machines. But these components are not soldered to the pads as yet. For that you need to put these boards in an oven that heats up the boards and melts the solder paste. The melted solder paste sticks the pins of the components to the pads when it cools down.
Ovens also come in automatic and manual forms. In an automatic system, you decide the environment setting and put the board in the oven. The board ejects after the required time automatically. In a manual oven, you set the temperature and put the board in and take it out yourself after an estimated time period. Fig. 4 shows a reflow oven and Table V lists some ovens from different manufacturers.
Though most people prefer to mount through-hole components manually but, for faster turnaround, a desktop wave-soldering machine can be used. These machines have melted solder in a flat bed, and the boards are moved over it slowly so the through-hole solder points catch some solder. The solder sticks the pins with the pads, making a permanent joint on cooling. Fig. 5 shows a desktop wave-soldering machine.
With all these equipment available, you can reduce the prototype-development time drastically. This, in turn, can reduce the time to market, increasing your product’s chances of being a success. If you do not want to spend money on all these equipment in one go, select those that you really need to increase the efficiency of your product development cycle.
The author is a technical editor at EFY