Customers often ask us about the manufacturing process for the motor control electronics we make so we thought we’d do a short blog article on this to give you a little more information. Keep an eye on our Youtube channel as we have a few behind the scenes factory tour type videos planned.
There are (broadly speaking) two types of components – surface mount (often referred to as SMT) and through hole (often referred to as TH). The clue is in the name with these – surface mount components sit on the surface of a PCB, bridging exposed pads on the PCB surface in order to create circuits. The through-hole components go through holes in the PCB and are then soldered on the underside of the board to create a joint. Filling the hole with solder then connects the component directly to the circuit.
The production process starts with bare PCBs, in other words a PCB that has not been populated with components. These are typically panellised to improve efficiency in the printing and placing processes later on. The first part of the process involves inspecting and cleaning these to ensure that they are free from contaminants and in good condition for production. Assuming they are, they are serial numbered and racked up ready for production.
The first stage of the production process involves printing the board with solder paste. This is done using an automatic stencil printer which loads the board and uses a custom stencil for each board to ensure that solder paste is placed on all the pads where it’s needed. The stencil also ensures that the correct volume of paste is applied in these areas and is an important part of ensuring the overall quality of the final product. Too much paste and there is a high risk of shorts, too little and there may not be an adequate solder joint to meet IPC standards and ensure a high quality, reliable performance.
Following a brief journey along a conveyor, the panel now arrives in the pick and place machine. This is the machine that everybody likes to watch as it can be mesmerising when in full flow. This machine uses feeders loaded up with components and placement heads on a gantry to move place components in the exact positions and orientations required for the board to be correct. The tackiness of the solder paste then ensures that they stay in place before going into the oven. We use a Samsung machine that runs with 6 heads and can place up to 18000 components an hour.
Again, the board will have a brief trip on a conveyor and will then move into the reflow oven. These are often compared with commercial pizza or bread ovens when the process is being explained to newcomers. The oven features several heated zones which can be directly controlled by the oven computer. These enable the operator to change the profiles on the oven in a way that perfectly manages the requirements of the board. A smaller, lighter board will not require as much heat as a larger heavier board for example. Equally, certain components may be particularly sensitive to heat and a lower profile may be more appropriate. It is common to change the profile settings for the oven from board to board in order to ensure the best possible finish.
At this point, the surface mount assembly is inspected based on the standards set out in the IPC-A-610 guidelines. These guidelines highlight 3 classes of electronics, Class 1, 2 and 3. All Zikodrive boards are manufactured to Class 2 as standard and certain products are Class 3 (the highest possible standard) if required. Inspection can be assisted with an AOI machine if required and all boards either pass or fail. Depending on the nature of the failure it is normally possible to rework or repair the board using rework stations. However, if a repair is not possible then the board will be scrapped. Those boards that pass – the vast majority – will then go to TH assembly if required or functional testing if there is no TH parts required.
Depending on the nature of the design, TH assembly can either be done using a wave solder machine, by hand, or using a soldering robot. If all TH and SMT components are on the same side of the board then the fastest method is usually the wave solder machine. This machine uses a conveyor to pass boards over a fluxer, pre-heat stage and a solder wave (a small wave of molten solder) that is calibrated to just catch the underside of the PCB without flooding the entire board in hot solder and ruining the assembly.
Where the assembly is double sided it is often not possible to use the wave solder machine in assembly and the work must therefore be done by hand or using the soldering robot.
On completion of the TH assembly, all boards are once again inspected in order to ensure that the TH solder joints meet IPC standards and that no issues have occurred during this part of the process. It is very rare for issues to occur here but on occasion the heat exerted on the board during this process can cause SMT components to move slightly meaning they may now fail IPC inspection. As with SMT inspection, where there are errors these can normally be cleanly reworked using a rework station or if there are significant issues then the board will be rejected.
The final stage of the assembly process is to flash the boards with the correct programme and run a functional test to ensure that all aspects of the board are working as expected. The test jigs for this stage are all customised to each board as the IOs, motor drive stage and various other functions are all entirely different. Controllers are placed under load and a range of checks carried out to ensure they meet the required specification. Any failures are inspected and potentially reworked or rejected depending on the nature of the issue.
Once the boards have completed this stage of the assembly process they are then assigned into stock and are ready for dispatch as required.
If you have any questions on the assembly process or would like more information about how we work then please get in touch with us and we’d be happy to help.