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Quick step in design

Prototyping is generally regarded as a critical part of the design process. It is the time when designers, for the first time, see their creations take physical form and, most importantly, the time when it starts to become apparent if these products work and can be made efficiently.

Fashions change and, for some designers, prototyping became unfashionable when it started being perceived as too expensive. Back in 2008, some companies, particularly small start ups, came under extreme financial pressure and began to cut out crucial prototyping steps. John Boston, managing director of Custom Interconnect (CIL), commented: "These smaller, more innovative, companies are trying to get off the ground and if there's a way for them to save some money, they'll try to do it. But things are a bit easier now and they have learnt that if you try and cut the corners, then generally something will go wrong."

The problem was the corner cutting could remove the prototyping stage altogether, or the design could move straight from first prototype into full production. "What we are seeing now is that, in every instance when that appeared to work, the product ultimately failed," added Boston. "For nearly four years, people got their fingers burnt in this way. But now it is returning to how it should be – doing prototypes, then maybe a 50 off pre-production run before committing to full production."

These fundamental engineering principles, according to Boston, are followed by such safety critical industries as military and oil and gas. "They do things a certain way – the right way – and don't deviate from it." However, newer, smaller companies fashion themselves on the virtual company model – they design, market and sell the product, but leave production and support to a third party – that may have lost touch with the engineering aspects."

Designers who download files and import them into their project may pass their CAD rules, but are surprised when the prototypes fail. Boston said: "You tend to find that, on the next design and the one after that, it is much better because you are feeding back production techniques and production materials and processes – you can take time out and cost out based on the knowledge of many years."

As the economy continues to recover, the financial pressure to take the short cuts may lessen, but the squeeze on time to market continues to increase. Usually, a project has a time scale – a new product may have to be launched or demonstrated at a particular exhibition or conference, or tie in with other events or programmes. Projects, say the contract manufacturers, invariably overrun and every extra day that is taken in engineering is a day lost in prototyping/NPI.

Hence the rise of services that go under a variety of names, but generally known as rapid prototyping. Sarah Keeley is sales and marketing manager at CSM Electronics, a contract manufacturer who offers such a service. "Although most bare board manufacturers offer the service," she commented, "a lot of CEMs now offer rapid prototyping as a value added addition to their existing full turnkey services, that can include PCB layouts, assembled PCBs, software development and programmed devices using either in house designers or working with a bare PCB supplier." It therefore has the attractive benefit of the project being managed under one roof, thus minimising the overall project turn-around time and maximising quality.

The first stage is to establish what the prototype boards are for. Datalink Electronics is another company offering its version – quick turnaround prototyping. Head of the design team, Arash Ghadar, pointed out the difference between boards intended to prove a concept and prototypes needed to demonstrate suitability for manufacture. In the former case, quality may not be as important as getting boards onto an engineer's desk quickly. If it is just trying out a new chip, then an evaluation board might be a cheaper route. "But," said Ghadar, "if you are prototyping to make sure the board is suitable for production, then you have to follow the normal production route as much as you can."

Ghadar believes prototyping is an important part of the design process. "We offer the prototyping service as part of design and it is usually a two stage process. The first prototype is to make sure that everything works. Then we take it through approvals; EMC testing and so on. It is likely that you will have to change the board and that becomes your second prototype. If, at that point, you can take this through the production line it becomes a production version."

CIL has just launched its Rapid service, partly to access lower volume markets and partly because it provides a better quality service for its customers. All electronics assembly machines and processes are fractionally different and CIL was finding that prototypes coming from elsewhere with a clean bill of health were providing slightly disappointing yields in their very early days of production. Boston noted: "Although we are using a separate department [for Rapid] with separate people, when we are doing prototypes, we talk internally about what happens if it goes to production, what can we add or do to help the design engineer create more of a production item."

So what about those times when speed is of the essence? Rapid prototyping sometimes creates an expectation of a 24 hour turnaround, but is that realistic? Keeley commented: "If all data is available – bill of materials, drawings, Gerber files – then, yes, it is possible." Boston claimed one of his customers came in with boards and components and left 49 minutes later with fully assembled boards. But it's not always so easy; the more complex the product, the more processes are involved and all take time. Getting the bare PCB fabricated often takes a day or two itself.

More significant is the impact of components with long lead times. A two day prototyping service will take 12 weeks and two days if there is a 12 week lead time on a component, so sometimes it is worth buying components during the design phase to avoid such delays. Boston said: "As soon as we get a bill of materials, we will advise what we can get ex-stock and what we can't. Sometimes you are only talking £3 for the components and you only want five, so for the sake of £15, you can compress that 12 weeks down to two days for the parts. 'Do you want to take the risk' – the answer is virtually always 'yes'."

While time is important the critical thing is to get it right – a production ready product. Ghadar summed up: "Getting the prototype done in five days, rather than 15, is important, but saving one or two days doesn't matter."

Author
Tim Fryer

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