Electronics Apps – Electrodroid

When I got my first Android phone it was suggested I look up an app called Electrodroid. After installing it, I was instantly impressed. Electrodroid is only available on Android and is the app to have for any and every kind of electronics engineer and technician. As shown above there are four tabs to choose a vast array of useful information that’s available on the go from your device.

Calculators – has a range of different calculators to help with everything from resistor codes to filters and PCB trace width calculation. All of this in one place.

The next tab has a whole list of

Pin-Outs – think of a connector used in everyday electronics – it’s probably here. On top of this are pin outs for Raspberry Pi, Arduino’s and Beaglebone boards also.

The next tab is a Resource table for component selection, wiring size tables and chip databases.


The amount information available to the Electrodroid user is massive and it’s accurate, quality information that can be relied on.

Electrodroid is also expandable, with a number of Plugins that are designed to work with it.

It’s when the plugin’s for Electrodroid are used that the true power of this little app becomes apparent. The plugins allow us to add extra functionality to:

  • Access a complete parts database.
  • PIC Microcontroller Database.
  • Atmel Micro Database.
  • Circuit Simulation.

That’s right – circuit simulation on a mobile device. While this may be hard to use on a phone, a 7 or 10 inch tablet offers a useable environment for this  feature.

The Circuit Simulator which is offered by Everycircuit and has in app costs up to £12.

As with many of these apps the basic version was free, with a paid version offering more features. The cost of the paid version only around £2 the investment is a no-brainer and easily worth more as the plugin features that can go with Electrodroid are free to use (apart from the simulator).

Access to an integrated electronics design assistant as powerful as this – How much can it change how engineer’s and technician’s work?

Circuit Mechanix © 2016

Assembly and Rework of Multilayer PCB’s

Multilayer PCB’s are being used in almost every electronic device that can be thought of. This is especially true in higher density electronic devices where components are crammed into the smallest space possible. The reason for this? It enables the engineer to track out the circuit in a tight area while providing functionality like impedance control.

Multilayer PCB’s also provide excellent thermal conductivity to be able to get heat away from components without the need of heat sinks.

This kind of approach is bound to have an effect on the way PCB’s are assembled and re-worked. Soldering parts down to a board can be hard enough, but getting them off again without damaging the board can be much harder.


Assembly and Reflow:

Applying the paste and placing components onto a multilayer PCB happens in the same way as a single sided PCB. The problems come during reflow. Imagine the PCB that’s being worked on now going through a big heater and being warmed up to a thermal profile like this one:

The area’s of copper that are larger are going to sap the heat away faster and will therefore take longer to heat up than the area’s where there is little excess copper. So all the different parts of the circuit are warming up at different rates. This could potentially lead to solder re-flow taking place at different times. This could lead to components tombstoning, reflow not taking place underneath IC’s with power pads and dry joints. Basically – a PCB engineer’s nightmare.

Compensating for this is usually done by increasing the dwell time (referred to as the soaking zone in the chart) the board is subjected to. This ensures that every part of the PCB is at the right temperature for the fluxes to start working and will reach the desired peak temperature, with all the solder joints forming as they should.

Another reflow process used is the vapour phase reflow process, where heat transfer liquid gasses are used to heat every part of the PCB and the components uniformly. The issue with the vapour phase process is that it’s not a mass production process and is often slower than using IR reflow ovens. The vapour phase process can damage some sensitive components, so make sure evert component is suitable.


Rework & Repair:

In order to carry our PCB repairs, two things are needed:

1)The right tools

2) A well trained / experienced operator

A good soldering iron like a Metcal system with interchangeable tips and a talon system are essential to carry out good re-work. The heat is used efficiently and the tips transfer the heat well. A good rule of thumb is to use the largest tip possible, particularly in the removal process. A talon system allows the operator to use different sized tips to ‘pinch’ the component on each side and remove very easily with no PCB damage incurred.

PCB damage during component removal is common, but with modern small pad sizes, not as easy to repair as ten or more years ago.So knowing how to get enough heat into the part without damaging it or he PCB is necessary.

When removing a part from the board, any kind of force will damage the board or the pads. Using a pair of tweezers or other removal tool the part should lift off with no effort. Taking time here and being patient will ensure a successful re-work.

Now for the tricky bit – what about if we’re trying to rework something without legs, particularly a component with a power pad on the bottom?

Getting heat into a multilayer board can be a real issue for re-work, the greater the layers, the more of a problem it is. This is because the copper in each layers saps the heat away from the part. We mustn’t be too critical, after all that what we want it to do! But when we want to re-work, this definitely bites us where it hurts. With a production board going into the field using a quality re-work station is absolutely the best way.

If the boards are prototypes and a fast re-work is needed, it’s useful to be able to do this in house. Some good tips for making this easier are:

1) A quality, temperature controlled hot air pencil is often enough.

2) If a pencil alone is not enough use a pre heater under the board to heat the re-work area.

3) Use a large iron tip to help pre-heat the specific component.

The basic thing to bear in mind is that more copper means more energy to heat a board or component. Designs are now in this catch 22 – like it or not!

Circuit Mechanix © 2016

Processes and pitfalls of multilayer fabrication every designer needs to know

Multilayer PCB’s are layers of copper area’s etched to their patters to form a single circuit that all connects together, just like in the design. Easy eh?

We wish!

When we scratch away at the process behind the design we lean that maybe all is not what we might think. Defining the stackup before routing even starts is essential. This is because the stackup will define where the designer can route, where ground and power planes are located and where any controlled impedances will be routed too.

  • Time spent at this stage isn’t wasted, it’s well spent as this can save time later in tearing up chunks of design work and starting again.
  • Being realistic about the number of layers will also be beneficial at this stage, this means balancing (as always) cost against technical performance.
  • Discussing the requirements with the fabricator at this stage means that this stage of the build is designed and we don’t have to mess with it later.

Copper balance is a factor to be considered that few outside PCB design and fabrication know about – yet with multilayer boards it can have a profound effect. The effect of bad copper balance is  a warped board and is caused if a board is designed with some areas of highly dense copper features where on other parts it’s less dense. Planes which over lap across the layers is often enough to cure this, either that or filling in between routed areas with ground pour. If doing this, make sure that no creepage distances, or other circuit features are compromised.

Drill holes and vias seem like a simple affair – on the whole they are. But when a plated hole is defined in your design – is this the size of the hole drilled or after plating? Normally this isn’t an issue, but if using custom assemblies with fine wires, problems can arise where the wire doesn’t fit in the hole as expected.

Pouring ground shapes – the design system needs to keep the features it creates large enough to be successfully etched. Tiny copper features can come adrift and cause circuit havoc. So as usual check what the fabricator can make and set the pour tool and DRC to filter any tiny features out – or a re-design is likely to follow sooner than expected.

Layer order. Every fabricator has their own default definition of layer orders.

Don’t assume that they’re all the same – make sure that each of the layers in the design are well labelled and the order of the layers is clear.

The effect of incorrect layer order may be a semi functioning circuit, but with controlled impedances referenced to power planes rather than ground, there may be some unusual and hard to find problems occurring.

As with everything in the PCB world, every part of the process has rules, processes and limitations. Knowing what they are and working with these processes is going to lead to better made designs.

Circuit Mechanix © 2016

 

Intercept Impedance Calculator

It’s not greatly known that Intercept, the company behind the Pantheon PCB / Hybrid design software had released a controlled impedance calculator for mobile and tablet.

The app is available for either Android or Apple platforms and the first impression is a clean, uncluttered look. There are seven basic options and each one brings up the required variables. The power of this app is in it’s ease of use, the user prompted for the required values.

Picture3

Where there is a calculator next to a value is where the user can leave the value blank. Input the other variables, press on the one remaining (which is shown in red) and there you go – your required value appears.

After diving into the other functions in the app the operation is much the same, the amount of variables change depending on what’s being calculated, but the user only needs to have a basic understanding to operate this and get a sensible answer.

 

The only thing I found was that the app defaults to mils dimensions automatically every time the app is used. I tend to work in metric these days, but it’s not a big deal, just mildly irritating.

I haven’t compared this to Polar or other high end software, but I have compared it against a few known  and is pretty accurate. This is a free app that’s meant to be a guide and not replace the likes of Polar. On that basis it’s a very useful tool for any PCB engineer’s toolkit.

Circuit Mechanix © 2016

Designing Multilayer PCB’s – What you need to know

Todays world of high speed, high pin count high power density electronics means designing multilayer PCB’s is almost essential for any design. Multilayer boards enable a designer to be able to integrate controlled impedances for high speed and RF circuits with power circuits easily and efficiently without taking up large amounts of space and eliminating the need to use jumper links to make connections.

But as engineer’s knowing how our multilayer boards are built is key to ensuring design success. Knowing the materials that will be used at the fabricator, so the right cores and pre-pregs are used is are particularly important for impedance control. Allowing enough time and effort to work out the number of layers required and their stackup will be time well spent. While this can be changed during the design, it may mean that other design elements will be affected and time wasted in re- design to account for this. So it needs to be planned well.

So, how does a PCB Designer work all of this out?

Layers – Deciding on grounding and power strategies will give us the best guide on the layers we need. Ask these questions:

1)How many ground planes needed? Are there different ground on different planes or are they split?

2)How many power rails are there? Is a layer being allowed for each power rail or are we splitting them? Will they be split into area above each other to stop ground bounce?

3)What and how many signals are there to route? Will there need to be signals routed on inner layers and will these need to be protected from the power layers?

4)Just a plain through hole board or are blind / buried vias being employed?

 


 

Plane Arrangement:

The plane arrangement is typically number of planes one on top of the other on different layers. They will be a mix of power and ground nets. This is an acceptable way to arrange power and ground planes.

However in order to minimise ground bounce in  a circuit, the power and ground planes could follow the same shaped profile on each layer, this reduces the coupling between power and ground. It could be any shape, but would follow the same profile on each layer for power and ground.

Note:

For ground planes it’s generally accepted that splitting planes creates signal integrity ‘gaps’. While sometimes it’s unavoidable to split a plane, if possible it’s best avoided.


 

Once the basis for the multilayer board is decided, talked over with the fabricator, the placement and routing can begin in earnest. Placement is one of the key elements in achieving design success – get it right and you’re a big step towards making routing much easier. The big question here is  – will there be components on both sides of the board?

Routing is next and is one of the elements of board design that can go wrong if not carried through methodically:

1) Ground comes first – always. If the ground connection is being made to an inner layer on a via, make the track thick – around 0.5mm and keep the via close to the component, particularly on decoupling components. For larger components make multiple ground connections, to give a low impedance connection.

2) Power – don’t underestimate this, get it right to avoid issues later, think about the power path. For example make sure the power connection flows from the plane to decoupling to component in that order. Not the other way around.

3) Controlled Impedances / Sensitive Signals – These signals are next in priority. The signals’ sensitivity will dictate it’s priority.

4) Everything else in it’s own natural order.

Following these steps should ensure the right circuit elements are routed with the right priority to achieve design success!

Finally, once all the connections have been made check the copper balance. Area’s of different copper density could cause the PCB to warp during fabrication. Filling in the blank area’s with ground pour where this won’t affect function or safety will ensure a uniform copper density and flat boards.

This of course is a list of the basic elements of multilayer design, but if the designer thinks along these lines and how the circuit will work before routing a single track – the path to success is less troublesome.

© Circuit Mechanix 2016

Circuit Mechanix June 2016

 

Circuit Mechanix Jun 2016

Welcome to the second issue of Circuit Mechanix, a magazine for the Printed Circuit industry in the UK.

This month’s issue is focussing on multilayer Printed Circuit Board and how the design can affect fabrication and assembly.

This issue’s review is on apps for electronics and PCB engineers, there are a number out there, but in this issue Electrodroid and Intercept’s Impedance calcualtor are looked at.

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 Jun 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