Defined Impedance Calculators

October 2, 2019/in Electronic Manufacturing Technology, Tips & Tricks /by Kevin Smith

There are many different Impedance calculators for PCB designers to use, some are free such as the one available to Eurocircuits customers and some you need to pay for a licence or a monthly subscription.

The aim of them all is to provide the necessary track/gap and isolation values for the layout and manufacture of your PCB.

The interfaces vary from one to another as does the way you input the parameters that are used by the calculator and this is where a user must take care.

Since the very successful launch of the Eurocircuits DEFINED IMPEDANCE pool service we have received feedback that results between our calculator and others varies.

This is something that we took very seriously and launched an investigation to establish why there was a difference.

What We Discovered

It turned out that the parameters required for one system were different to another. For example, the value H1 in our calculator is not the same as H1 in another calculator.

In the example below it is in fact the H2 in the other calculator.

In addition, the H2 value in the other system is actually equal to H1 + T in our calculator as above.

Therefore, adding the same values for H1 & H2 in the Eurocircuits calculator compared to another may very well deliver different results, as the corresponding input parameters may differ.

To verify that the Eurocircuits calculator provides the correct results we ran several tests:

Firstly, we used the same parameters in our calculator and the Altium calculator and as expected the results we different.
We then corrected the parameters used in the Altium calculator to what they require (e.g. H1+T) and the results were extremely close (Zdiff = 100.035E vs 99.146463E).

It is important to use the correct dielectric constant (εr) value for the selected material.

This value will change depending upon the selected frequency.

In the Eurocircuits calculator all the known values are automatically updated based on the selected build-up.

Another point to be aware of is how the calculator generates the results. Is it calculated using the correct formula or simply using a known ‘Rule of Thumb’ equation?

For example, a ‘Rule of Thumb’ equation for a Differential Impedance value is 2x that of the Characteristic Impedance value.

This is only a rough and non-mathematical value which may vary significantly from the real value.

It is important to check how these values are derived?

Conclusion

When using an impedance calculator, you must ensure that the actual values entered, correspond to the parameters required and are not simply copied from one calculator to the next:

Eurocircuits’ Impedance calculator uses real values as defined in the supplier’s data sheets.
Eurocircuits also calculates the correct Differential Impedance values using the correct formula and not a ‘Rule of Thumb’ method.

Finally, all calculators provide theoretical impedance values as they cannot take in to account the variables and tolerances of the manufacturing process.

This means that whilst the calculator gives you a value, the actual value measured on the PCB may well be different.

It is Eurocircuits’ experience that the measured values on the PCB are within a ±10% of our calculated values.

Selecting the Right Surface Finish for Your PCB

April 14, 2019/in Tips & Tricks /by Kevin Smith

To protect the copper solder pads on a PCB from oxidation, contamination and to enhance their solderability, they need to be protected with a Surface Finish and these must conform to the European Union RoHS & RoHS2 (Restriction of Hazardous Substances) Directives.

But which is the right Surface Finish for your PCB’s?

In accordance to this directive Eurocircuits offers the following Lead-free Surface Finishes:

Hot Air Levelling or Hot Air Surface Levelling (HAL or HASL).
Chemical Ni/Au (Electroless Nickle/Gold – ENIG).
Chemical Ag (Immersion Silver).
Electroplated Ni/Au (Hard Gold) for Edge Connectors.
Carbon (Chemical C) for Switch Contacts.

Each has its own advantages and disadvantages and the goal is to select the one that best fits you the Function and Usage of the PCB.

For more information please read our post Selecting the Right Surface Finish for your Design.

Another important point about Lead-free soldering this that it requires higher soldering temperatures which have a direct effect on the reliability and durability of your PCB.

For more information please read our post on How Often Can You Raise a Eurocircuits PCB to Lead-free Soldering Temperatures.

The Eurocircuits Team.

Selecting the Right Surface Finish for your PCB

April 14, 2019/in Tips & Tricks /by eC Admin

Surface Finishes on Printed Circuit Boards

Choosing the right Surface Finish for your PCB is as important as choosing a manufacturer to make the PCB.

Use the wrong Surface Finish and it you may have downstream issues during assembly or longer-term reliability issues.

The Surface finish is a protection against the elements, in short it is designed to protect soldering pads and contact pads from oxidation or becoming contaminated.

Without a Surface finish the exposed copper would oxidise, thus making the soldering of components difficult and any electrical contact pads such as edge connectors would have a poor electrical connection.

Since all finishes have advantages and disadvantages, it is important to select the right one based on the PCB design, storage, functionality and how they will be handled during assembly.

The different finishes we offer are Lead-free Hot Air Surface Levelling (HAL), Electroless Nickel/Immersion Gold (ENIG) and Immersion Silver (ImAg). All of these are Lead-free and can be used for RoHS designs as well as in a SnPb assembly.

It is recommended that edge connectors have an Electroplated Hard Gold (Ni/Au) surface finish.

Any Lead Free

If you don’t select a finish then your PCB’s will be produced on a panel with either a Lead-free HAL, chem. Ag or chem. NiAu. The finish will be defined by other PCB’s on the same panel.

However, if your design includes fine pitch pads this will automatically be changed to ENIG finish.

HAL Leadfree (Hot Air Surface Levelling)

The Lead-free HAL (or HASL as it is also known) finish provides the PCB with the highest level of solderability. It also provides the level of robustness with regards to multi-step assembly and storage at a reasonable price.

On the other hand, the HAL process requires the submerging of the complete PCB in liquid solder and thus is responsible for extra thermal load on the PCB.

For that reason, it isn’t the best choice if your board requires small via holes or the board exceeds a normal thickness (when the aspect ratio is high).

Another aspect of this surface finish is less flat than other surface finishes, although we try to achieve the flattest surface possible.

The varying amount of solder present on the component solder-pads may also make this finish less suitable for components with small and fine pitch pads.

Chemical Ni/Au (Electroless Nickle/Immersion Gold or ENIG)

Many customers choose this surface finish as it offers a flat surface, good solderability and acceptable shelf life.

It is a well-established surface finish for PCB’s having been introduced even before the requirement for Lead-free assembly. However, the ENIG process is complicated with a higher risk of defects (skip plating, black pad or interface embrittlement).

When using ENIG, the solder-joint is formed between the solder and the Ni layer of the NiAu surface, not with the underlying Cu. The Au is completely dissolved into the solder joint.

Also this interface seems to be considerably more brittle than with the HAL (SnCu) interface.

It is not recommended for applications which are subject to shocks, bending or strong vibrations.

One final point, it is the most expensive surface finish offered, however, for some applications, like key pads or wire bonding, it is the best solution.

Chemical Ni/Au Large Area (Electroless Nickle/Immersion Gold or ENIG)

Any copper area that is not covered by Soldermask and is ≥40% of the total copper area of an outer layer is classed as a larger area.

These will increase the cost of the PCB.

Chemical Ni/Au before Soldermask (Electroless Nickle/Immersion Gold or ENIG)

If this option is selected then the ENIG surface finish is applied before the Soldermask and all copper will be covered with ENIG.

Chemical Ag (Immersion Silver)

This surface finish is often a bone of contention, some love this finish, and some hate it.

It offers a flat surface with very good solderability. The solder-joint is created with the underlying Cu, since the Ag is dissolved during soldering process.

It all sounds good, but the ImAg is susceptible to sulphur dioxide (SO²) which tarnishes the surface and creates the AgS² layer. This layer affects adversely the solderability.

To avoid this tarnish, we pack the PCB’s in silver saving paper and hermetically sealed packing to avoid moisture and atmosphere SO² coming in.

In case of multi-step assembly, the partially assembled PCB’s should be stored in a sulphur-free atmosphere.

Depending upon the storage conditions the shelf life of this surface finish maybe an issue.

Other Available Surface Finishes

Hard Gold for Edge Connectors

Due to the need for edge connectors pads to be resistant to abrasion we recommend that these have an electroplated NiAu (Hard Gold) surface finish.

This finish is processed in a specialised bath that is only used for these type of connectors.

It is not possible to have this hard gold processed on other locations of the PCB.

Carbon

Carbon combines a high mechanical strength with a good electrical conductivity and can often be used as a substitute for gold on contacts.

It is printed directly on the Cu and used for switch contacts, foil keyboards and can enable the creation of cross-over conductors. It is resistant to HAL and soldering processes without showing practically any change in resistance.

Summary Table

Copper and the Board Edge

March 22, 2019/in Tips & Tricks /by Kevin Smith

Copper and the Board Edge.

There are three options under our Advanced options heading which may be confusing:

Copper up to board edge
PTH on the board edge
Round-edge plating.

Here’s how to sort them out.

Copper up to Board edge.

To avoid damage to the copper during the profiling operation we normally ask for a minimum distance between the copper features and the edge of the PCB. This distance is:

0.25 mm on outer layers with breakrouting
0.40 mm on inner layers with breakrouting
0.45 mm on all layers with V-cut scoring.

These figures are needed to accommodate industry-standard manufacturing and machining tolerances. For V-cut scoring it is also necessary to accommodate the V of the cutter.

Sometimes it is necessary to run a copper plane up to the board edge. In this case select “Copper to board edge”. There is no extra charge for this but it alerts our engineers to set up a different cutter speed.

“Copper to board edge” should normally only be used for planes and large copper areas where any slight damage to the copper will not impact on the performance of the PCB.

Tracks must not be placed within the minimum distance of the board edge where they could be damaged. Our engineers will raise an exception whenever they find tracks within the exclusion zone.

If we find pads within the minimum distance of the board edge, we will clip them back to restore the minimum copper-free space unless:

the pads are part of an edge connector (usually with a bevelled edge)
the pads are marked as “up to the board edge” in a separate mechanical layer
the clipping is more than 25% of the pad surface in which case we will send an exception to the customer.

NOTE.

Copper to board edge cannot be combined with V-cut scoring.

PTH on board edge.

Also called “castellated holes”.

These are plated holes cut through on the board edge and used to join two PCBs either by direct soldering or via a connector. As the process requires extra steps, plated holes on the board edge are a cost-option.

Your data should clearly show the holes and the profile. Ideally include the information in a mechanical layer.

TIPS.

There must be enough spare space on the edge of the PCB for us to hold the PCB in the production panel during manufacture. If you need castellated holes on all 4 sides, email us your design or proposed profile as early in the design process as possible. We can then confirm that it is manufacturable or suggest any necessary changes.
You must have pads on top and bottom layer (and on inner layers where possible) to anchor the plating securely to the PCB.
As a general rule the holes should be as large as possible to ensure good soldering to the mother PCB. We recommend 0.80 mm and above. Minimum end size possible is 0.5mm.
All surface finishes are possible but our preference is for selective gold over nickel for the smaller sizes.

Round edge plating.

This means that most or part of the edge of a PCB or a cut-out is plated from the top side to the bottom side.

This may be to ensure a good ground to a metal casing or for shielding purposes.

To manufacture a board with round-edge plating we rout the board profile where the edge plating is required before the through-hole plating process. This involves extra process steps so round-edge plating is a cost option.

TIPS.

Where the board edge is to be plated there must be copper on the top and bottom layer with a minimum width of 0.5mm from the edge of the board inwards.
As we need to hold the circuit within the production panel during processing we cannot plate round 100% of the edge. There must be some gaps so that we can place rout tabs. If you need a very high percentage of edge-plating, email us your design or proposed profile as early in the design process as possible. We can then confirm that it is manufacturable or suggest any necessary changes.
Indicate clearly in a mechanical layer where you need round-edge plating.
Selective chemical nickel-gold is the only surface finish suitable for round-edge plating.

Tips & Tricks – Why Do Components Tombstone

November 29, 2018/in Tips & Tricks /by Super Admin

Tips & Tricks – Why Do Components Tombstone

Ever wondered what is Tombstoning and why does it happen?

What is Tombstoning?

Tombstoning also known as the Manhattan or crocodile effect is where one end of the component lifts from a pad of the PCB during reflow soldering process and affects mainly surface mount components such as resistors, capacitor and inductors.

Why does it happen?

There are a few reasons for Tombstoning such as the soldering process, contamination of the PCB or the actual PCB Layout.

When soldering a component to a PCB it is important that solder reaches the ideal fluid state, this is known as the Wetting of the solder.

It then forms an inter-metallic bond between the terminal of the component and the pad on the PCB before it cools and becomes solid.

Tombstoning occurs when one end of a component (like a resistor) completes the Wetting process before the other. This end then pulls and tilts the component to create the Tombstone effect.

The PCB Layout can influence the Wetting process. An imbalance of the thermal mass between component pads will result in one end completing the wetting process before the other.

At Eurocircuits we continue to develop our Tools, Information, and Guidelines to help PCB Designer Engineers to create ‘Right First Time for Manufacture’ PCB Layouts.

Why not take a few minutes to review our latest Guideline on Tombstoning.

Take a look at some of the exciting Projects that were presented @ Electronica 2019

Should you have any questions about any of our services, please feel free to get in touch via email, telephone or instantly with our online chat during office hours. We will be more than happy to help.

Why not follow us on our social media, keeping up to date with all of our latest news?

News & Information

For many years Eurocircuits have provided you with important News & Information about our services, products, free to use smart tools and the Electronic Manufacturing World. Take a peak at what we offer:

Eurocircuits company update. This section contains updates and information about the Eurocircuits Group. As a valued partner you will receive updates and news covering our company activities, team news and business developments etc.

Events & Workshops. Eurocircuits is an active participant of events and exhibitions, it also organises events, sbinars and workshops, especially concerning technical topics

Tips & Tricks.The electronic value chain starts with a design and then converting it to a digital form. This section covers all design related issues, their influence on manufacturing.

Electronic Manufacturing Technology. Eurocircuits goal is to inform all Electronic Designers about Electronic Manufacturing Techniques and processes. Whilst, this may start with PCB manufacturing it also covers the Assbbly, Testing and Housing etc…

Online Smart Tools – Services & Products. All Eurocircuits customers have access to an online customer account and through this, access to our Smart Tools and services. This section covers User Guides, updates and new features and tools etc. It will help you to optimise your knowledge, use of these tools and the electronic manufacturing services and products we offer.

Customer Applications & Student Projects. Eurocircuits actively encourages its customers to share their experiences with other customers. In addition to this, we support many student projects and inspire thb to write about their adventures and the technology they have designed.

eCvelo. Next to being an Electronics Manufacturing Company, Eurocircuits also has a heart for clean mobility. As result we have developed and are building trike and quad cycles with a covered frame. Keep updated by opting in to this section.

Eurocircuits TV

	Eurocircuits TV is Eurocircuits’ media channel bringing electronic designers and others video news and VLOGs about our electronic manufacturing world.

Tips & Tricks: Avoiding Solder Escape/Wick during Reflow

November 13, 2018/in Tips & Tricks /by Super Admin

Avoiding Solder Escape/Wick during Reflow

Have you ever wondered why sometimes you have poor Solder joints on your PCB’s!

One of the main reasons is that the Solder Paste flows away from the pad on the PCB during Reflow, this is known as Solder Escape, Solder Wick or Solder Drainage.

Why does this happen, well there are a few reasons but inevitably they are all the result of Thermal Dissipation during the Reflow process. Basically, the heat flows away from the pad on the PCB to a larger Thermal conductive area that’s connected to the pad and unprotected by a Soldermask Dam, these include:

Via Holes
Copper Areas
Larger Tracks

Below is an example (animation) of a Via Hole that is too close to a SM pad and therefore has no Soldermask Dam to stop the Solder Paste escaping into the hole.

There are several solutions to this issue and Eurocircuits is developing a PCB Assembly Guideline to help Designers understand and creating PCB layouts that may create potential Assembly issues.

Please visit our PCB Assembly Guidelines section on Solder Escape/Wick for more information on how to avoid this issue.

Should you have any questions about any of our services, please feel free to get in touch via email, telephone or instantly with our online chat during office hours. We will be more than happy to help.

Why not follow us on our social media, keeping up to date with all of our latest news?

News & Information

For many years Eurocircuits have provided you with important News & Information about our services, products, free to use smart tools and the Electronic Manufacturing World. Take a peak at what we offer:

Eurocircuits company update. This section contains updates and information about the Eurocircuits Group. As a valued partner you will receive updates and news covering our company activities, team news and business developments etc.

Events & Workshops. Eurocircuits is an active participant of events and exhibitions, it also organises events, seminars and workshops, especially concerning technical topics

Tips & Tricks.The electronic value chain starts with a design and then converting it to a digital form. This section covers all design related issues, their influence on manufacturing.

Electronic Manufacturing Technology. Eurocircuits goal is to inform all Electronic Designers about Electronic Manufacturing Techniques and processes. Whilst, this may start with PCB manufacturing it also covers the Assembly, Testing and Housing etc…

Online Smart Tools – Services & Products. All Eurocircuits customers have access to an online customer account and through this, access to our Smart Tools and services. This section covers User Guides, updates and new features and tools etc. It will help you to optimise your knowledge, use of these tools and the electronic manufacturing services and products we offer.

Customer Applications & Student Projects. Eurocircuits actively encourages its customers to share their experiences with other customers. In addition to this, we support many student projects and inspire them to write about their adventures and the technology they have designed.

eCvelo. Next to being an Electronics Manufacturing Company, Eurocircuits also has a heart for clean mobility. As result we have developed and are building trike and quad cycles with a covered frame. Keep updated by opting in to this section.

Eurocircuits TV

	Eurocircuits TV is Eurocircuits’ media channel bringing electronic designers and others video news and VLOGs about our electronic manufacturing world.

Tips & Tricks – BOM & CPL Data

October 2, 2018/in Tips & Tricks /by Super Admin

Tips & Tricks – BOM & CPL Data

It has been over a year since we launched our Prototype & Small series Assembly service.

One question that we are often asked is, what information must you our customer supply for the Assemble service.

To answer this question, we need the BOM (Bill of Materials) and CPL (Component Placement List) data.

These files are usually generated by the CAD system and output in an ASCII format, the format varies from one CAD system to another however, it is the information contained within these files that is important.

The BOM must contain the information below:

MPN (Manufacturers Part Number) or Supplier Part Number.
Full Description of the Part (including value where applicable)
Component Reference Designations that use this Part.

Addition information that is also very useful:

Manufacturer
Supplier

Below is an example of a BOM file.

It is important that each line that contains a Component Reference Designator also contains the required part information.

Using the CPL we automatically superimpose the components listed in the BOM to the PCB, allowing the verify the component placement on the PCB.

The CPL file must contain the following information:

Component Reference Designator (e.g. C1, L2, R3 etc).
X and Y Position of the component Center.
Orientation
Side (Top or Bottom).

Great news for KiCAD and Eagle users as the CPL data is already contained within the .BRD or .KiCAD file.

Below is an example of a CPL file.

For more information concern BOM and CPL files please visit the Eurocircuits PCBA Visualizer – user guide and the Eurocircuits Guide on How to Upload or Import BOM & CPL files into the PCBA Visualizer.