Featured Article: Fabrication pitfalls in making smaller PCB’s

The thing with making PCB’s smaller – is that everything gets smaller. It sounds obvious but this is the cause of the issues with getting smaller PCB’s or more densely packed PCB fabricated.

The issue is that every detail is smaller and more prone to error in the manufacturing process. Resistor pads for 0402, 0201, or the tiny pads of a BGA are smaller than what would be possible from mainstream fabricators twenty years ago. In those days such details would have been the kind of detail that would have been fabricated out and yet now engineers want it made, with a solder resist aperture and plating  with gold. With this is the other issue with making the circuit tiny. The 0.3 / 0.4mm hole used for via’s is now far too big. Nowadays a 0.2mm hole or smaller is frequently used, enabling components with 0.5mm pitch pins to be routed out without much difficulty.

Smaller holes are required if designs are to pack in all the connections they need. The plating and aspect ratio of these holes needs to be taken into account – this affects the entire design of the PCB. These issues are enough to give even the experienced PCB engineer a headache. In order to get the design right for fabrication the whole deign from the stackup upwards needs considering.

In every PCB design there are tiny details that exist, some my flag up as design rules and some might not. Slivers of solder mask that have been processed in the design could cause havoc with solder pads if they were made and came adrift. There has to be that decision about who’s going to remove them in the processing – the fabricator or the PCB designer. The fabricator should be able to process these small features out  – but if they get missed it could mean trouble.

The same can be true of copper features caused when creating copper pours and plane layers. Tiny features can come adrift in processing and cause connections to short, making a circuit useless. Getting rid of them at either end will save a huge amount of strife.

While testing and inspection at the fabricator can pick up shorts in a circuit the best approach is to give the process every chance of being able to make a good PCB without errors occurring. Testing and inspection is not 100% accurate, especially with the human factor involved. When faults are found after the board has been assembled more time and money has been wasted on something potentially very simple that could have been avoided.

The key is making sure the design and review process for a design is robust enough to pick up issues and to make good decisions on what to do about them. Sending PCB design’s out and keeping your fingers crossed usually results in a cross boss that wants to know why good money has been wasted.

Knowing and understanding the mechanics involved in PCB fabrication and how these will be applied to designs that are created is essential to knowing the right questions to ask any one involved in the fabrication processes. It’s hopeful to think that questions will be raised when issues are encountered, but this isn’t reliable.

It’s better to make sure there are as few questions as possible to be asked before the design is released – or do you trust your fabricator(s) that much?

Circuit Mechanix © 2016

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Review: Snap EDA

A few years ago I found out about a project being undertaken called SnapEDA, which aims to bring accurate and detailed library components to PCB design tools. The idea is to save time for the PCB / electronics engineer making library components and bring them the parts they need across a range of different design tools.

The idea came from Natasha Baker who started Snap EDA to address the market of delivering PCB library components to engineers quickly and cost effectively.

The website gives a library of parts in it’s database, a design hub from semiconductor manufacturer’s, a diagnostics tool for natasha-baker-e09d3bd73a63checking library parts and a community to share key topics with other engineers.

Each part in the SnapEDA library has it’s own symbol, PCB footprint and parts. 

data downloaded straight to the engineer when they need it for free. Snap EDA’s components are available in formats that can be used by all of the main PCB EDA providers. And are constantly looking to expand the range of components they offer and the range of tools that can be provided for. 

Labelling itself as the universal parts library their features and rate of progress means that this title is well deserved. By interacting and addressing the needs of electronics and PCB engineers there may soon be a time when spending hours making library parts could be a thing of the past.  

Into this mix SnapEDA just just launched a new feature into it‘s cluster of useful and innovative services – Instapart. The engineer can request a part for $29 or the part and it’s 3D model for $79 and is delivered for download within 24 hours.

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When considering the time it takes to create complex components like IC’s $75 for a full part in 24 hours saves time and a lot of money. The engineer is concentrating on design aspects as they should be rather than taking precious time in creating the part for their library.

Have a look at the website – www.snapeda.com have a look and see if they can transform library creation for you.

© Circuit Mechanix 2016

The Challenges of Designing Smaller PCB’s

The PCB designer is our hero in this story and hero’s never get an easy ride. This story involves the evil manager of the PCB designer walking up to him one day, possibly with the even more evil mechanical engineer in tow. The PCB engineer’s next task is to re-design a board that they’ve put blood, sweat and tears into and make it even smaller, based on the mechanical engineer’s drawings.

Happy that this task has been offloaded the evil manager and mechanical engineer disappear, leaving our hero to work out how to do this.

Sounds familiar?

But what does our PCB engineer do next? The chances are that this isn’t small reduction, they’ve not messed about and want it half the size. Because the mechanics have already been made there’s no chance of negotiation.

The first thing is to go back to the engineer – what can be cut out of the design. Every component counts and spare connectors can free up lots of room. Once the circuit has been agreed and all the necessary working out of what the circuit needs to do has been worked out there’s the next step.

Components: Most components come in more than one package type these days – selecting the one that’s going to be the right fit is easy. Making sure it’s available and still meets cost restrictions can be harder.

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PCB Strategy: Before starting any design work having a design strategy is going to save messing about later in the process. Every detail that can give or take space needs considering.

Layers: Estimating how many more layers will be needed ensures the design can be completed, too many will add unnecessary cost.

Track and gap:

Reducing the track and gap can have a big impact on saving space in a board design. If the components are being reduced in size then it makes sense to reduce the track and gap in line with this. Check to see what the fabricator can  achieve before committing and see what the cost / yield implications might be.

Via’s:  Via’s can suddenly seem huge when using smaller components. See what the fabricator can make as a minimum, making sure the aspect ratio is achievable.

Annular ring: If there are any plated through holes in the PCB design, reducing the annular ring can help add some much needed space. 2 x the drill hole diameter is accepted as the standard, however 1.5 x the drill diameter is typically the minimum that should be used.

Silk Markings: So after all of this there still is nowhere near enough room to squeeze everything in. Component references on the silk screen are very useful, but they do take up a lot of space. A component reference for an 0402 component would need to be about twice as big as the component to be readable.

If the naming strategy hasn’t been created well the component reference can dwarf the component. So getting rid of them on the board  will save a lot of space. Make sure there’s a well checked and marked assembly drawing for the PCB – fault finding will be pain as it is, don’t make it harder!

Now our hero the PCB designer has worked out how to work the impossible there are still issues that can foul things up. EMC, thermal considerations and creepage and clearance are just some of them. Assembly issues can arise from shrinking a design too and that’s before testability and service and rework problems.

When shrinking the size of electronics there are always compromises and they’re usually sent down the process chain. This is almost unavoidable.

© Circuit Mechanix 2016

Circuit Mechanix September 2016

 

circuit-mechanix-sept-2016

 

Welcome to the third issue (and a bit late I might add) of Circuit Mechanix, a magazine for the Printed Circuit industry in the UK.

In this month’s issue the general theme of this issue is making electronics smaller, what needs think

This issue’s review is SnapEDA – the universal parts library.

Have a look – get in touch and get involved if you like. This is a young project and help with news and features is needed.

 

 

Download the PDF for the magazine here:

circuit-mechanix-sept-2016

I’m still not able to provide a flip book – as soon as I get over this technical hurdle I will let you all know!

There is also a LinkedIn Group for the Magazine and discussion around it here:

Circuit Mechanix LinkedIn Group