Board technology; where are we now and what does the future hold?
27 June 2016
As Newbury Electronics prepares to celebrate 60 years of PCB production, Philip King, Managing Director, takes a look back at how the requirements and production techniques have evolved, before providing a few reminders about what designers must consider to ensure they get the best produced board possible.
(Click here to view article in digi-issue)
Finally, the article examines what might lie ahead in terms of board technology and production techniques.
It is over 150 years since the first electrical connection boards; metal strips mounted on to wooden boards, were produced. Jump forward a hundred years to the 1950s and this is when Newbury Electronics entered the electronics market, undertaking secondary machining on carburettors and providing circuit boards to the AWRE (Atomic Weapons Research Establishment) and ICL (in its former guise as Leo Computers). These boards consisted of 'an electrical path created directly on an insulated surface by printing the required layout with electronically conductive ink'. At this time, the boards were only single sided but by the early 1970s double sided boards were being produced.
Another 20 years later and CADCAM technology is being used with multi layer circuit boards becoming the norm during the 1990s. Despite predictions that everything would fail as the millennium arrived, technological and engineering innovation continued and pick and place production was followed by surface mounted production techniques. The last 15 years has seen any company that is really serious about the PCB market invest in laser imaging, digital ink jet printing, SMD placement machines, laser cut solder past, and x-ray based inspection techniques.
Where are we now and how does it impact the electrical design engineer?
Electrical design engineers are making their own lives and those of their PCB manufacturers harder by not recognising how a poorly designed board can impact on the board's production and its ultimate viability. Ever more complex circuits and systems obviously require meticulous thought and planning but the same level of diligence needs to be applied to the design to ensure that the latest production techniques can be applied to deliver a board that meets the most stringent requirements. Looking at the designs they receive, the team at Newbury Electronics estimate that approximately 50 percent of them would benefit from some modification that would improve the manufacturing process.
First and foremost, PCB designers need to design for manufacture. This means that they need to understand the various processes involved and take them into consideration. One of the first factors is the balance of the weight of the copper across the board; when evenly distributed, copper will plate evenly as well as give a uniformly thick copper surface layer. This means the printing element of the PRINTED circuit board (the clue is in the product name) is far more effective, be it legends, solder resist or solder paste.
It is very hard to print effectively on to a rough surface and quality will suffer. In addition, plating resist will not strip properly if an area of isolated copper is over plated, creating potential short circuits. Even distribution of copper on the PCB contributes to an even thermal mass, also helping to permit an even spread across the board temperature profile during solder paste reflow. If solder paste melts and solidifies unevenly, SMD parts can “tombstone”, lift, or move during reflow causing serious and unnecessary assembly defects.
Looking back 150 years, those predecessors of modern day PCBs were mounted on wooden frames to give them form. With today's trend for ever smaller and more complex boards, those without handling frames and sufficient fiducials will often find that their accuracy has been compromised. Boards submitted for manufacture without a frame may take up to 50 percent longer to produce, which inevitably has a knock-on financial implication.
For optimum efficiency through the manufacturing process, boards should be within an A4 handling frame, anything larger is liable to flex and require manual intervention at some stage in the process. On a smaller scale, anything less than 80mm x 80mm will be too small for the vast majority of automated machines. In the last 10 years, part sizes have reduced by a factor of five and there is no doubt that smaller boards do offer a cost saving as they use less laminate.
Those pioneers of the electronics industry could probably not envisage it as it is now, with an estimated 5 million parts to choose from for inclusion on a board. Checking, checking and checking again against recognised industry databases to ensure an accurate BOM is the next requirement of the modern electronics engineer. Omitting a digit from a part number may mean that the final board won't function, assuming that it can be made. Incorrect or absent part details add unnecessary delays and incur additional costs. Closely allied to the accuracy of the data is the accuracy of the CAD data; as components become ever smaller, manual selection is not viable, however, the automated machines that now fulfil this role are only effective if the data they are fed is exact.
When asked to envisage a PCB most people will have a picture of the green board with numerous copper and black coloured wires and components. However, with the increasing inclusion of LEDs on boards, white solder, which can actually improve the performance of the LEDs, is appearing more often. Whilst this is acceptable for these specific components it should not be used more widely as optical inspection equipment is optimised to operate with a green resist; an excess of white solder has the effect of 'blinding' the camera thus reducing the effectiveness of the solder evaluation process.
If the engineer has managed to combine their electronics expertise with a sound knowledge of the production requirements the finished board will be successful. The manufacture also wants to be sure so their final commitment is to the highest level of quality control and inspection, and this is where some of the most advanced technology is coming into play with the installation of high resolution x-ray verification equipment.
So, what of the future?
It is estimated that sometime in 2016, the number of connected devices will overtake the number of people on the planet for the first time. Each and every one of those devices will require a PCB. Calculations by Gartner, the US market research company, reveal that last year around five billion devices, including smartphones, tablets, smart electricity meters, cars and factory machines were able to communicate via the Internet and this figure is expected to rise to between seven and eight billion.
According to figures provided by Tridonic, analysts are already talking about 24 to 35 billion connected devices by 2020 and the implications for the PCB market of growth on this scale are vast. BI Intelligence expects total expenditure on hardware, application development and system integration to reach 6,000 billion dollars in the next five years.
Just as those early pioneers could probably not have envisaged electronic devices that we now take for granted so it is for us today when we think about the future. Wearables and other new products and solutions that are still in the design stage will be upon us in far less time that we might expect and PCB design and manufacture will need to respond. Miniaturisation will continue but at the same time the boards will become increasingly complex. This will require an increase in the number of layers in a board but not an associated increase in thickness nor a compromise on the board’s physical strength or functionality.
Technological developments that are already being explored in the aerospace and military markets will spill out into wider commercial applications and will utilise new approaches. These are likely to include the evolution of thick and thin technologies, embedded actives and the use of new substrates that will further enhance PCB performance.
There is no doubt that this is an exciting time for the electronics industry and that PCB designers and manufacturers are going to be pivotal in how it responds to the opportunities and challenges of the next 50 years.
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