Prototyping of electronic devices using SMT assembly in the Comarch IoT Plant

Prototype building is an important yet problematic business area for electronics manufacturers. Fierce competition and increasing customer demands are forcing us to act faster and work even more efficiently. The time available for the design phase is shrinking significantly, and the preparation of a prototype in short-run production requires a reorganisation of processes not only in the factory but also throughout the company. This is why more and more companies are looking to collaborate in this area. This kind of support is offered by Comarch IoT Plant, providing rapid prototyping and electronic device assembly services (EMS, Electronic Manufacturing Services).

What is electronics prototyping and why is it challenging?

Building a prototype is part of the wider electronics design process. It acts as a control phase between the preparation of the virtual design and the series production itself. The dynamic development of technology combined with the trend towards miniaturisation of electronic devices requires investment in the prototyping stage, impossible without the right infrastructure. This means that manufacturing companies are forced to commit a lot of resources to preparing just a few prototype printed circuit boards (PCBs, Printed Circuit Boards). It is a process involving numerous attempts and analogously mistakes. The logical way to meet this challenge is to outsource the assembly. 

– “95% of our production is related to short-run prototyping, in volumes of up to a few dozen units. Our customers often have their own highly advanced factories. However, even in such cases, launching the batch size 1 production to create a prototype would require wider changes in the organisation of the plant's work. For example, isolating a separate production line that usually operates 24/7 for volume production” – says Piotr Sieńko, SMT Process Leader at Comarch IoT Plant.

However, this is not where the prototyping challenges end. The initial batch of PCBs requires a stop to test the functionality and commissioning of further modules of a particular device. If everything works correctly, the production can be continued. In practice, however, it is much more complicated.

– ”A common situation at the design stage is to make a lot of changes, so assembling prototypes right up to the end of the process involves implementing custom solutions. Manufacturing companies cannot afford downtime in factories caused by successive modifications to prototypes. Working with an external technology partner on short production batches ensures such flexibility. Sometimes a customer will require a single board to be produced which they need to run and test to make sure the equipment is working properly. Such tests mostly take place at the customer's premises, but we are also able to set up a suitable site at our factory as part of the accelerated production process. Only when the customer is assured that everything is working properly, we are given the go-ahead to continue production of a batch”– adds Piotr Sieńko.

Available assembly methods for electronic prototypes 

There are two commonly used methods for assembing electronic components on a PCB – through-hole technology mounting (THT) and surface-mount technology (SMT). The first, the THT, uses PCBs with special holes through which leads in the form of wire feet are threaded and then soldered. It is a time-consuming process, requiring manual work by the operator. Another one, the SMT, allows for working on the PCB surface, where components are placed with the help of specialised, pre-programmed machines. 

The surface mounting is slowly displacing the older through-hole solution as it offers many more advantages, the most important of which are:

• assembly speed,
• possible automation of the production process,
• miniaturisation of the target electronic devices and achieving a high component distribution density,
• mounting of components on both PCB sides,
• low connection impedance resulting in better electrical properties at high frequencies,
• greater mechanical resistance to shock and vibration due to the low weight of the components,
• the option to combine machines into a single, continuous production line,
• 2in1 – SMT assembly can also be used to fit through-hole components (pin-in-paste process).

Process flow for manufacturing prototypes in SMT assembly

Even before starting SMT production, a strategically important step is to collect and analyse technical documentation in order to prepare the control software for the automatic machines on the production line. The documentation should include files such as:

• BOM (Bill of Materials) – a list of all the components to be included on the PCB,
• Gerber – a virtual image of the PCB from which individual templates are ordered for the printing of solder paste, the binder that connects the board to the SMD (Surface-Mount Devices) components specified in the BOM,
• Pick&Place – containing the co-ordinates for each designator,
• Assembly diagram – defining parameters such as polarity, component orientation or non-standard assembly solutions (e.g. additional Kynar wire connections, soldering one component on another, etc.)

– “Documentation at the prototyping stage takes the most diverse forms. It is often delivered literally days before the actual production. I am aware that customers’ engineering teams operate under enormous time pressure and sometimes projects wander between different departments. There are instances where discrepancies between individual files will be found in the documentation. We try to find all the differences and give the customer feedback as soon as possible. We are very sensitive to analysing this stage as thoroughly as possible, as this avoids surprises during production, which could in turn generate additional costs associated with, for example, the reworking of a circuit“ – comments Piotr Sieńko.

This documentation makes it possible to plan the subsequent manufacturing process, which consists of assembling the electronic components onto a PCB. The following stages can be distinguished:

1. Laser marking of PCBs to give them a unique identifier.
2. Printing of solder paste with an air-tensioned stencil.
3. Stacking of components using Pick&Place machines.
4. Soldering in a reflow oven.
5. Quality control of the assembly with the aid of automatic optical inspection (AOI) or, if necessary, X-Ray and CT scans.

Conveyors between the successive machines on the production line that move the wafer to the next stage. They can be automated, but during the assembly of prototypes, additional optical inspection by operators also between the different parts of the process proves useful. All stages of assembly are equally important, but two of them deserve special mention for the overall process to be successful.

 – “Step two, which involves printing the solder paste using a special stencil, is crucial, as any problems we fail to detect here (e.g. too much paste causing short circuits) will affect the rest of the process. In addition to that, step four, reflow soldering, which requires setting the right temperature profile, is important. There are seven heating zones in our oven. The first five zones are preparatory zones, and in the next two the actual soldering of the joints takes place” – explains Piotr Sieńko.

A specific preheating profile is selected for the product. Why?

– “The components vary in size, weight and coverage, some heat up faster, others more slowly, so quite a long preheating is needed for all of them to reach the target temperature. It is also about the gradual heating up of the solder paste itself, which includes a tin and silver alloy, but also a flux that has defined activation parameters. The effect of accelerated flux activation will be increased voiding, i.e. the formation of excess voids in solder joints, the permissible number of which is strictly defined by standards” – adds Piotr Sieńko.

Comarch IoT Plant – rapid prototyping services and much more 

Outsourcing the prototyping of electronic devices using SMT assembly brings many business benefits, even for companies with advanced manufacturing facilities. Quick access to machinery, flexibility in terms of the solutions used, reduction in the time required for assembly, elimination of the cost that would have to be incurred in reorganising production processes in their own factory and the ability to concentrate on their core business are the key advantages of this approach. Before deciding on a technology partner, however, it is worth looking at their experience and the quality of the services they offer.

In operation since 2017, the state-of-the-art Comarch IoT Plant not only offers high-quality services in rapid prototyping and product development, but also in the area of electronic device assembly (EMS) and post-production quality control. Our long years of experience in research and development (R&D) and electronics manufacturing enable us to provide products, EMS services and design of the highest quality, in line with current standards and trends.