Panel editor

  1. Panel editor – the next level of efficiency in PCB Visualizer

“I want my boards delivered as a panel, but I need to see what it looks like before I place my order”

“I want to make sure that I have got the maximum number of circuits on my assembly panel”

“My assembly people need fiducials and tooling-holes in exactly the right place.  I haven’t got time to make a drawing, but they want to check the panel’s OK for them before I order.”

Eurocircuits have always had options to deliver a customer’s circuits in a panel (see our Panel Guidelines), but there has never been an opportunity to see the panel before placing the order, to experiment to find the best circuit “fill”, or to order a special layout without providing a drawing.  The new PCB Visualizer tool, Panel Editor, changes that.  Now you can view the Eurocircuits panelisation you have specified before you place your order.  Or, if you need a special panelisation, you can create your own panel directly on-screen.  Place your order confident that what you have seen or what you have laid out is what you will get as your finished panel – and there will be no delays while our engineers query your requirements.

How do I …..?

  1. Use PCB Visualizer Panel Editor to get a fast price without uploading data?
  2. View or modify my eC-panel by Eurocircuits?
  3. Make a custom panel?
  4. Set up/change panel and board properties?
  5. Change the step and repeat values?
  6. “Fill” a panel?
  7. Define special panel settings (stepped blocks, rotated circuits/blocks, custom blocks e.g. “nested” for L- and T-shaped circuits?)
  8. Add my own border features (tooling holes, fiducials, text etc.)?
  9. Specify panels with several different circuits (multipanels)?
  10. Get confirmation I did it all right, even if I did it for the first time? Use our pre-production approval process.

Our BLOG explains it all and contains 2 movies to illustrate the processes.

See separate sections for each topic.  If you have any questions, use our online chat line to talk to one of our engineers.

1. Use PCB Visualizer Panel Editor to get a fast price without uploading data?

Most Panel Editor options can be used before you upload your data.  For this, PCB Visualizer  uses dummy PCBs.

There are three panel options.  To select one, go to the Delivery format box at the top of the screen.  For more details of each, see our Panel Guidelines.  Selecting eC-panel by Eurocircuits or Custom panel by Eurocircuits automatically opens the Panel menu.

delivery format

eC-panel by Eurocircuits

Specify the repeats you want in X and Y.  Select the panel border, and the PCB spacing from the pull-down boxes.  All eC-panels are eC-registration compatible.  This means that they have the necessary tooling holes in the border if you want to use a solder-paste stencil with our eC-stencil-mate or eC-stencil-fix.  As they also have our standard pattern tooling holes and fiducials in the corners (see Panel Guidelines p. 6), they are 100% suitable for use with other registration systems.

Click Panel editor to see the panel with the dummy PCBs.  For the full range of options, see below.

Customer panel by Eurocircuits

Click the Panel editor wizard and proceed as below to specify the step and repeat, border and separation distance required.  Ignore the red warning message about the 0,0 panel size – this will be changed by the Panel editor.  PCB Visualizer will display the default board size, so for an accurate price enter the correct circuit size, make any other size changes required and click Apply.

TIP: Don’t put in the border elements at this stage as they will be lost when you upload the real board data.

Customer panel by customer.

Use this panel option if you have already prepared Gerber files with the complete panelisation for a special layout or for a multi-panel (panel with several different designs).  Your layout should meet our panelisation requirements for panel border and distance between the circuits.  This option won’t open Panel Editor as the files will display correctly in PCB Visualizer.

TIP: All delivery panels require a border to hold them together during transport and handling.  If you have not included a border or want to put additional features into the border, select Custom panel by Eurocircuits and specify a 1-up panel using the Panel editor wizard.

2. View or modify eC-panel by Eurocircuits

Step 1.  Load the job into PCB Visualizer.

Use the “Price Calculator” option to get a price and then upload your data.  Or choose the “Analyse your data” route, so that PCB Configurator fills out the board parameters for you.  Go to Shopping basket and click the PCB Visualizer column for the job you want.

Step 2.  View eC-panel by Eurocircuits.

If you have already specified the step and repeat, border size, PCB separation method and distance, click the Panel editor wizard to see the panelised circuit.

NOTE:

The router path is shown as a hatched area.  Our engineers will place rout tabs in this area to ensure a stable panel.

TIP: If there are areas in which you do not want rout tabs to appear due to sensitive components etc., specify them in a mechanical drawing.

You can now change:

  • Repeat in X and/or Y
  • PCB separation method
  • Panel border
  • PCB spacing

For any other changes, click “Advanced panel options”.

Click “Apply” at the bottom of the screen and the price in PCB Configurator will automatically update to the new configuration.  Click the orange “Save changes” box to update the basket.

price summary

In the next menu just click Continue.  There is no need to re-upload the job.

MOVIE: create and view an eC-panel with panel editor

 

This film gives an overview of how to make an eC-panel with our new panel  editor module, part of our PCB Visualizer software.

YouTube settings

You can always view this video in full screen mode by clicking the right symbol  on the navigation bar and upgrade the resolution by clicking the setting symbol .

3.  Lay out a custom panel by Eurocircuits.

TIPS:

  1. For hints and tips on designing stable panels including panelising round circuits and handling overhanging and heavy components, click here.
  2. If you are using an external assembly company and they supply a detailed dimensioned drawing of their requirements, you may find it easier to use the Launch inquiry route to get a price.  Upload your single circuit data, the drawing and your step and repeat instructions (as a README file) and our engineers will lay out the panel and give you a price.  This may take up to 1 working day.

PROCESS

Step 1.  Load the job into PCB Visualizer as Section 2 step 1 above.

Click the Panel editor wizard.  Ignore the red warning about the 0,0 panel size – the Panel editor will complete the correct size.

Step 2.  Select your panel border and enter your preferred value:

Step 3. Set up the circuit separation method and spacing:

Step 4. Choose the panel content type.

Select:

  1. Stepped PCB if you want to build your PCB out of single circuits.
  2. Stepped block if you want to build your panel out of a custom block of two or more interlocked or “nested” circuits, typically L- or T-shaped.  For this option, see below.

Step 4. Select “Stepped PCB”. And click “Next >”.

Step 5. Set up the basic step and repeat, and the rotation if required.  Additional options will be available in the editor.

Step 6. PCB Visualizer now shows the board together with top and bottom birds-eye view, the Panel and board properties menu and the panel tools menu.

  1. Swap top and bottom views by clicking on the bird’s eye menu, or using the tool menu icon.
  2. Pan and zoom with your mouse or use the pull-down zoom menu.

Click the orange “Apply” button to accept the panelisation and go back to the PCB Configurator menu.

4. Change panel and board properties.

Use this menu to change:

  • Panel size.
  • Panel border
  • Board separation method
  • Board separation distance

Or to add eC-compatible registration holes if you want to use a solder-paste stencil with our eC-stencil-mate or eC-stencil-fix.

TIP: If the board size is incorrect, PCB Visualizer will show a dummy panel.  Correct the size in the menu (“Board size”).

5. Change the step and repeat of the job

Click within the existing stepped circuits to select the block.  This opens the “Stepped PCB properties” menu.  You can now change the repeat and the rotation of the PCB.  Use to action

6. To “fill” a panel

  • Un-tick the Automatic X and Automatic Y boxes in the “Panel and board properties” menu.
  • Select the panel size you require (e.g. the Eurocircuits recommended maximum panel 350 X 250 mm, or your assembly company’s maximum size e.g. 300 x 200 mm)
  • Use the “Step/repeat block properties” menu to change the step and repeat and rotation to find the best fit
  • Re-click the Automatic boxes to get the final panel size.

7. Define special panel settings.

  • Stepped PCB
  • Stepped Block
  • Block (Custom block of nested PCBs: L-shapes, T-shapes, etc…)

These allow you to customise your panel layout.

Tools

 

TIPS:

  1. To deselect a tool, double-click the Select button or pick the next tool.
  2. To select a border element that is below another border element, you need to click with the right mouse button to first highlight it (orange border), then you can click with the left mouse button to select it.
  3. Use “Reset the panel definition” to
    • restart the Panel wizard – select “Create new panel definition”
    • clear everything and go back to the PCB Configurator menu – select “Clear panel definition”

7.1.  Add stepped PCB pattern

TIP: Use this function to step and repeat PCB blocks or to add rotated PCBs.

  1. Click the tool “Add stepped PCBs”.
  2. Select the orange location box where you want to repeat the same circuit pattern.
  3. This opens the “Stepped PCB properties” menu.  Enter the repeat values you require and click the location boxes as required.TIP: By default PCB Visualizer will retain the last repeat values used.  If these are incorrect, simply change them and the screen image will correct automatically.
    .
  4. Add spacers as required to control the distance between the blocks. Click “Select the object to edit” to clear the location boxes and show the true distances.TIP:The spacers change the distance between the blocks of circuits, not the individual circuits.  Change the distance between circuits in the “Panel and board properties” menu.

7.2.  Rotated blocks:

There are two ways to panelise with rotated and non-rotated circuits depending on your requirements.  To build a panel with rotated circuit patterns, follow the procedures here.  To put rotated and non-rotated in a set, see below.

  1. Click the tool “Add stepped PCBs”.
  2. Select the orange location box where you want to add the rotated pattern
  3. Enter the required repeat and rotation values


  • Add a spacer to control the exact distance between the blocks.

 

7.3.  Panelise with stepped blocks (“nested” PCBs).

Use this function to interlock (“nest”) L-shaped or T-shaped PCBs.

  1. Open the Panel editor
  2. Select the border required
  3. Set your preferred PCB spacing and separation
  4. Set the Panel content type to “Stepped Blocks”
  5. Click “Next>” to open the “Edit block definition” box.  Click “Edit block”.
  6. This opens the editing screen.
  7. The offset will normally remain at X = 0, Y = 0 for the first circuit.  For the demo job, change the rotation to 180°.
  8. To add a second circuit, click “Add a PCB”.  To avoid a second circuit being placed directly over the first circuit, it is given a notional offset, roughly 20% of its X & Y dimensions.
  9. Add the desired offsets for the finished set. Click Apply to return to the wizard.
  10. Click “Next>” to move to the “Define step values menu”.  Enter your preferred repeat and click “Finish”.

7.4.  Add a spacer.

Use this function to increase the width of a single border or the space between blocks of circuits.

  1. Select “Add a spacer” tool.
  2. Click on the orange locator box where you want to insert the space
  3. Enter your chosen spacer value.
  4. Click on “Select the object to edit” or “Apply” to show the new image.

TIP: Tick the Automatic box if you have a fixed panel size which the circuits do not fill exactly and you want to maintain e.g. the relationship between the circuits and the panel edge.  The automatic spacer will push the circuits into the required position.

8.  Define customer specific border elements.

TIPS:

  1. To see how these different options work together, see the illustration of an eC-panel above or the finished panel at the end of this section.
  2. All border elements are dimensioned from 8 reference points.  These are placed in the middle of the laminate border in the 4 corners and on the centre line of the panel.  For each tool click the tool, select the (first) reference point, and the tool menu will open.
  3. Border elements (except drill holes) can be placed on copper, soldermask or legend layers, and on top, bottom or both sides.

8.1 Add a drill hole border element.

  1. Select the “Drill hole border element” tool and the reference point.
  2. Enter the drill hole diameter plus the copper, soldermask and legend clearances and any offset required.
  3. Click to insert the hole.  Select the next reference point – the values entered will carry over.

8.2 Add a frame border element.

 

Specify the width, the side and the layer required (copper, soldermask and/or legend). Unless an offset is specified this will appear in the centre of each border.

 

8.3. Add a clearance border element.

 

Tooling holes, fiducials and text come with automatic clearances to your chosen values.  Use the clearance function if you need to clear copper, soldermask or legend for any reason.  The cut-off allows the corner to be rounded.

8.4. Add copper pad.

 

For example as a fiducial.  You can specify the pad size, the clearances from copper, soldermask and legend, and the offset from each reference point.

 

8.5. Add text border element.

 

 

 

Enter the text, dimensions, layer (copper, soldermask or legend), and the clearances required.  The cut-off value gives a curved clearance.  The soldermask and legend clearances will default to the copper values but they can be changed if you prefer.

8.6. Add hash fiducials

 

You can set copper, soldermask and legend clearances for hash fiducials.

 

8.7. Finished panel

Including eC-compatible tooling holes

 

MOVIE: use panel editor to create your own custom panel

 

This film gives an overview of how to make a custom panel using our new panel editor module, part of our PCB Visualizer software.

You can always view this video in full screen mode by clicking the right symbol  on the navigation bar and upgrade the resolution by clicking the setting symbol .

9. Specify panels with several different circuits (“Multipanels”)

PCB Visualizer has been developed as a Gerber file analyser to run Design Rule (DRC) and increasingly Design for Manufacturability (DFM) checks on single circuits.  There is at present no functionality to allow you to import and place interactively separate circuits into one delivery panel.

If you want to put several different circuits on one delivery panel, you have three options:

  1. Prepare a single Gerber file for each layer including the circuits you require in the positions where you want them in the panel.  Make sure that you provide a suitable border and distance between circuits. More …

    TIPS
  • You can use PCB Visualizer to analyse the panel as though it is a single circuit. If you need to add a border or border features, load the job as a 1 x 1 Customer panel by Eurocircuits.
  • To ensure optimum manufacturability we have rules for the maximum size and copper balance for panels with multiple different circuits.
  • Use the Launch inquiry route.  Upload a single .zip file including separate .zip files for each circuits and an exact drawing how you want them panelised.  Our engineers will check the data files and build the panel for you.  We will send you a quotation and you will be able to see the finished panel in PCB Visualizer.
  • Place your order and upload a single .zip file including separate .zip files for each circuits and an exact drawing how you want them panelised.  Skip PCB Visualizer.  If you want to check the panel before it goes into production click the box “Request pre-production approval” in the Running menu.

10. Pre-production approval

Not sure about the panel you have created and need reassurance before your panel goes into production? Use our pre-production approval check. More info in our BLOG.

Blind and buried vias

Blind and buried vias Blind and buried vias are used to connect between layers of a PCB where space is at a premium. A blind via connects an outer layer to one or more inner layers but does not go through the entire board. A buried via connects two or more inner layers but does […]

How often can you raise a Eurocircuits PCB to lead-free soldering temperatures?

By Dirk Stans – Eurocircuits and Geert Willems – Center for Electronics Design & Manufacturing, imec

References.

[1] PBA Design-for-Manufacturing Guideline EDM-D-001: PCB Specification, imec-cEDM, July 2013.

[2] IPC-4101C: Specification for Base Materials for Rigid and Multilayer Boards

[3] Geert Willems, Piet Watté, Predicting PCB delamination in lead-free assembly, Global SMT &
Packaging, Vol. 10, No. 9, September 2010, p. 10.

Situation today!

  • We live in the lead-free soldering era
  • Soldering temperatures are higher than before (+25-35°C)
  • Five years experience with lead-free soldering of FR-4 boards has revealed advantages and disadvantages
  • The quality and reliability of your product is critical for its success in the market-place
  • These factors make the choice of PCB laminate base materials increasingly important
  • But how do you as a PCB designer make an informed choice?
  • And how can you design robustness into your PCB to ensure optimum quality during assembly and reliability during the whole envisaged product lifetime?

First reaction!

There are a host of material parameters to consider for the current generation of PCB designs:

  • T260, T288
  • CTEz
  • Td
  • Tg
  • Moisture absorption

They determine whether or not your PCB will delaminate and the vias will survive the lead-free assembly conditions applied to your PCB.

How do you select the right combination for your design?

One could select the best possible value for each parameter but this limits the number of available materials considerably. Furthermore, these materials have their own disadvantages such as a poor manufacturability and brittleness.

What are the consequences? Is your problem solved?

  • If you select non-standard materials with unnecessarily high thermal performance requirements a way too expensive PCB is the result.
  • Your board supplier may not stock the material you have specified.
  • The material manufacturer may cease production of less frequently used materials.

=> Your PCB supply is expensive and not future safe.

 


To provide a cost effective and scientifically sound solution to its customers Eurocircuits partnered with imec’s Center for Electronics Design & Manufacturing. The methodology presented here is described in detail in PBA Design-for-Manufacturing Guideline: EDM-D-001: PCB Specification, developed by imec/cEDM and available at www.edmp.be. Parts of the guideline are reproduced here with permission of imec/cEDM.

Better start from what you know and can control!

Your product will be soldered lead-free so you need lead-free soldering compatible FR-4. The requirements for the PCB laminate depend on:

  1. How many times your PCB will be raised to lead-free soldering temperature during fabrication and assembly or “how many soldering cycles will your board need for assembly and possible repair?”.
  2. The maximum operating temperature for your application.
  3. The planned lifetime of your application counted in number of thermal cycles.

Your internal or external assembly partners should be able to provide the answer to the first question. Your customer or the end-user is the source to find the answer to the other questions.

Possible fabrication and assembly soldering cycles

How to determine the number of soldering temperature cycles to a PCB? The answer is given in the table below, Ref. [1].

The PCB fabrication and assembly processes given in the first column determine the number of solder cycles to be taken into account.

Process Cycles Explanation
HAL lead-free (bare board) 2 One HAL dip + one extra dip
Reflow 1
Wave soldering 1
Selective soldering 1 Including manual soldering
Touch-up / repair 1 Removing shorts or opens on leaded components
Component replacement 3 Removal+clean+re-solder: valid for using local heating

Specifications of lead-free soldering compatible FR-4

Always start from an internationally accepted standard. The IPC standard that defines lead-free solderable FR-4 is IPC-4101C:

  • There are 14 classes of lead-free compatible laminates: /99, /101, /102,/103[WG1] ,/121,/122, /124, /125/126,/127,/128,/129,/130,/131, each with slightly different properties.

More detailed information can be obtained via www.ipc.org

  • Key parameters:
    • Decomposition temperature: Td (Thermal decomposition temperature: see further)
    • Time-to-delamination: T260, T288, T300 (Time to delamination at 260°C, 288°C and 300°C; see further down)
    • Z-expansion (thickness direction): coefficients of thermal expansion alpha 1 and alpha 2 (ppm/oC), and CTEz the z-expansion in % between 50oC and 260oC

Rather than specifying a base material to your PCB supplier, check that his materials conform to one of the IPC defined classes and see what minimum values he guarantees for these key parameters. Your boards will be cheaper and available faster.

Let”s compare the SnPb era FR-4 against the lead-free compatible FR-4 in respect of these key parameters.

Typical values of SnPb-era FR4 laminate materials compared to those of the lead-free compatible FR4 classes .

FR4 SnPb

99

101

121

124

126

129

122

125

127

128

130

131

Td (°C)

+/-300

325

310

310

325

340

340

310

325

310

325

340

340

T260 (min)

2-15

30

30

30

30

30

30

30

30

30

30

30

30

T280 (min)

>10 sec

5

5

5

5

15

15

5

5

5

5

15

15

CTEz (%)

+/-4.5

3.5

4.0

4.0

3.5

3.0

3.5

4.0

3.5

4.0

3.5

3.0

3.5

As the table shows, there are significant differences between older FR4 and current lead-free solderable FR4s (shown in IPC classes) for the key parameters Td, T260, T288 and CTEz.

We now solder 25-35°C hotter than in tin-lead solder times. This causes risks for:

  • Delamination: parameters T260, T288 and to a lesser extent Td.
  • Via cracks: parameter CTEz

Let”s further examine the effect of these parameters.

Delamination

  • Driving force:
    • Laminate decomposition
    • Moisture within the PCB[1]
  • Key parameters:
    • Time-to-delamination: T260 – T288 – T300
    • Decomposition temperature Td
  • Failure types
    • “blisters”
    • High Ohm resistance shorts
    • Track failure (open circuit)
    • Via cracking (open circuit)
    • Field failure (usually not detectable during PCB assembly testing).

 

 

Delamination (extended separation inside the PCB)

Not more than 25 % of the distance between adjacent conductors or plated-through holes.

Not more than 1% of the printed wiring area on each side may be affected.

No propagation as a result of thermal stress testing or representative condition.

 

(6A) shows separation between two glass weave layers in the base material. The separation can also occur between the base material and the copper foil.

(6B)
shows a separation between individual layers.

(6C)
and (6D) show separations between laminate and internal or external pads respectively, or copper planes.

 

 

Key specifications of FR-4 with respect to temperature behavior

  • Decomposition temperature – Td
    • Measured using TGA: Thermo-Gravimetrical Analysis
    • The decomposition temperature Td determines how fast your board starts to degrade during heating. On reaching the Td temperature after heating up at a speed of 10°C/min, 5% of the base material will be decomposed. Since lead-free soldering needs temperatures about 25°C hotter than before, we need Td values for our material that are higher than before.
  • Time-to-Delamination: T260-T288-T300
    • Measured using TMA: Thermo-Mechanical Analysis
      T260-T288-T300 determine how long your base material can resist these temperatures before the material starts to delaminate (the material will increase in thickness).

Cycles to delamination as a function of laminate properties

Research and modeling by imec-cEDM has proven, Ref. [1, 2], that the IPC /sheet boundary conditions – especially the fixed T260≥30min does not provide sufficient protection to delamination. The following IPC-4101 compatible definition of thermal performance classes guarantees the indicated number Nd of solder cycles without cohesive[2] delamination, Ref. [1]. Note the more stringent T260 and T288 requirements.

 

Category

Td (°C)

Min. v

T260 (min)

Min. v

T288 (min)

Min. v

CTEz (%)

Max. v

Nd

Potentially compliant

IPC-4101 sheet numbers

Basic

310

30

5

4

7

99, 101, 102, 103, 121, 122, 124,

125, 126, 127, 128, 129, 130, 131

Mid

325

50

10

3.5

12

99, 102, 103, 124, 125, 126, 128,

129, 130, 131

High

340

80

15

3

20

102, 126, 130

 

A mid performance material with a T260≥50min and a T288≥10min will be able to withstand at least 12 solder cycles before delamination will occur in the bulk of the laminate assuming the PCB is dry. The physico-chemical mechanism links Td, T260 and T288. Therefore, the actual Td value is not an additional parameter.

Graphs to determine the number of solder cycles to delamination for a given combination of Time-to-delamination and decomposition temperatures are given respectively in EDM-D-001 and Ref. [2]. A calculation tool is available at www.edmp.be (free use for cEDM members).

Via cracking

A via crack is usually caused by the difference in thermal expansion between the laminate and the copper barrel of the hole. This is influenced by the thickness of the board, the thickness of the copper plating and the diameter of the hole. The key material parameters for this is the CTEz value.

  • Driving force:
    • Difference in CTE between the laminate and the copper plating of the via.
  • Key parameter:
    • CTEz: 50-260oC. The higher the expansion the worse the situation is.
  • (Tg, α1, α2) (Explanation further down in the text)
  • Failure types
    • Apparently open solder joint (especially BGA)
    • Intermittent open connection
    • Open via connection
    • Field failure (often not testable during manufacture)
    • Reduced PCB lifetime

 

Via cracks due to thermal stress can appear during soldering or during the operation of the board. Soldering stress cracks are tested by repeated soldering and for operational lifetime one tests this effect through accelerated thermal cycling testing (typical -40oC/125oC).

Let’s concentrate on the most critical effect of temperature cycling: z-axis tension in the via barrel due to the much larger Coefficient of Thermal Expansion CTE of the laminate in the z-axis compared to the CTE=17ppm/oC of copper.

CTEz, α1, α2: expansion in z-direction

 

 

 

The material parameter that has the biggest impact on cyclic tension in the z-axis direction is the CTEz value.

In the graph above you can see the relationship between the z-axis expansion of the material (CTEz) and temperature. The expansion is a rather linear process but has a click point where the angle of the curve changes and the z-axis expansion increases faster per °C. This click point is at the Tg value of the base material. It is actually the way the Tg is determined using Thermo-Mechanical Analysis (TMA).

The graph also shows that a traditional FR-4 material with Tg=150°C (orange line) has a CTEz value which is a lot higher than for the new lead-free solderable material (light green line) with the same Tg value. This is achieved by reducing the CTE of the laminate through the use of inert fillers (increases drill wear!) or/and using higher functionality epoxy types (harder, more brittle materials).

Conclusion: CTEz is far more important than Tg with respect to z-axis expansion. A higher Tg material does not guarantee a higher thermal performance with respect to lead-free soldering. However, it will increase the PCB cost.

 

 

Via crack model

According to EDM-D-001, 4.4.3, Ref. [1], plastic via deformation dominates under soldering conditions. Therefore, the via lifetime (number of solder cycles to failure) depends mainly on the CTEz value of the laminate. The small dependency on the via dimensions can be neglected for specification purposes. EDM-D-001 provides CTEz based criteria for selecting laminates that will provide sufficient number of solder cycles to via failure.

Eurocircuits materials with a maximum CTEz=3.5% guarantee conservatively less than 1% via failure after 14 solder cycles.

Note that under soldering conditions the vias are stretched by several percent which is a very large mechanical load knowing that via barrels will immediately fail when stretched by 7 to 10%, Ref. [1], Appendix B.

Via: operational reliability – number of -40/125oC cycles to via-failure

Under operational conditions the dimensions, board thickness and plating thickness may have a significant impact on the lifetime. In general the stress increases and thus the lifetime decreases with increasing board thickness, decreasing via diameter and decreasing plating thickness. Imec/cEDM developed an accurate analytical model to calculate the via strain during thermal cycling and to estimate the via lifetime.

The graphs below show the dependency of the via strain under -40/125oC cycling for a laminate with a1=50ppm/oC, an board thickness D and via diameter d for t=20μm (left) and t=10μm (right) via plating. (FEM: numerical Finite Element Modeling results)

 

Using the Wöhler relationship which relates the number of cycles to failure to the cyclic strain on the vias the lifetime of the vias under different operational conditions can be calculated. An online via lifetime calculation tool is available at www.edmp.be (free for cEDM members). An offline version for embedding in PCB design tools is available from imec/cEDM.

Impact of soldering on the life expectancy of the PCB: via degradation

As mentioned before soldering imposes very large stresses on the vias. When the via does not fail during soldering – which is off course the intention – the lifetime of the PCB vias is reduced after soldering compared to the lifetime of vias of an unsoldered board. EDM-D-001 explains how this effect can be calculated. Again, selecting materials with a low CTEz reduces the impact of the soldering on the via lifetime.

If we look again at our standard value CTEz of 3.5% we achieve less than 4.6% loss of life expectancy per applied solder cycle, EDM-D-001, 4.4.4, leading to an overall lifetime reduction for an unrepaired PBA between 13 to 20%.

Eurocircuits pooling panels.

The vast majority of our orders are produced on pooling panels.

The standard technological values for these boards are:

– board thickness 1.6mm

– minimum track & gap 150µm

– smallest hole size 0.25mm

– minimum copper plating in the holes 20µm

 

Based on these values and imec/cEDM’s methodology described in Ref. [1] and explained above, we have determined specifications for the base material we use.

 

Our goal is to offer our customers a guaranteed performance for our PCBs during their assembly processes and sufficient PCB reliability for medium operationally stressed electronic assemblies.

How often may you heat up your PCB to soldering temperature?

  • Pooling – minimum material specifications and maximum number of solder cycles
    • T260 = 60min, T288 > 10min & Td = 325°C =>16 cycles
    • CTEz = 3.5%
    • 1.6mm PCB => 14 cycles 1% failure or 11 cycles 0.1% failure
    • 20µm plating
    • Tg 145°C=> max operating temp 120°C
    • Eurocircuits wants to be on the safe side => -2 cycles
    • Lead-free hot-air solder-leveling involves => -2 cycles
  • So, using our minimum guaranteed material specification, a standard Eurocircuits pooling PCB with lead-free HAL finish may be raised to the lead-free soldering temperature (=<260°C) during assembly 10 times – on condition that the PCB is sufficiently dry[3].
  • The PCBs maximum operational temperature is 120°C.
  • In fact, the materials we currently use, Isola IS400 and Nan Ya NP-155F, perform much better than our minimum guaranteed specifications. They have the values: T260=60 minutes, T288>10 minutes, Td=350°C, CTEz=3%, Tg=145°C. CTEz=3% would bring the basic number of solder cycles already to 20 with 1% failure instead of 14 cycles.
  • Via reliability decreases over time and with every applied solder cycle (for example, 8 cycles at 4.6% adds up to +/-37% loss of life expectancy).
  • For better reliability use large vias and limit board thickness. The laminate CTEz and the CTE below Tg a1 are the dominating via reliability parameters.

“hot” – “hotter” – “hottest”

Like any good steak, any good PCB can be burned!

This article is made with the support of:

Imec’s Center for Electronics Design & Manufacturing
Kapeldreef 75
3001 Heverlee
Belgium

Geert Willems – 0498 919464 – Geert.Willems@imec.be

 

 


[1] Moisture absorbed into the PCB can exacerbate delamination and, due to the higher soldering temperature, has become a much more critical parameter than it was with SnPb solder. It can be countered by storing PCBs in a temperature and humidity controlled environment. As moisture, if present, would be a local variable, we have not considered it further in our discussion of material properties.

[2] Cohesive delamination: delamination in the bulk of the laminate as opposed to delamination at the resin/copper interface.

[3] Moisture absorbed into the PCB increases the tendency to delamination due to the additional internal stress of the water vapor pressure. This can be countered by storing PCBs in dry bags or low humidity (<5 RH%) dry cabinets.


The smallest possible distance between two holes

What is the smallest possible distance between plated through holes?

A. The holes are a part of different electrical nets?

Plated through holes that belong to a different electrical net, need at least 0.25mm base material between their hole walls. To calculate this, you will need to count with the manufacturing tool size which is 0.10mm larger than the end diameter.

 


A 1.00mm PTH finished hole size, is drilled with a 1.10mm tool. So to leave 0.25mm of base material between two holes of 1.00mm their centre coordinates need to be 1.35mm apart. Or in other words: two PTH holes from a different electrical net need to be 0.35mm from each other, measured on the finished holes size (end diameter).

Why do we need this distance?

Smaller than 0.25mm drill to drill distances will create micro cracks along the glass fibre walls. The chemicals used in the galvanic line can intrude these cracks and create small shorts between the hole walls. The resistance of these shorts is typically larger than 1 MOhm.

Why could we use a smaller distance in the past?

In the past (before 2006) the distance could be smaller because we used only base material for leaded PCB technology. The materials for lead-free PCB technology are more brittle and thus more sensitive to cracks and moisture intrusion.

B. The holes are a part of the same electrical net?

When the plated through holes are part of the same electrical net, the PCB designer may decide that the possible shorts described under point A above are not causing any problems. In that case we are able to produce these neighbouring PTH holes with a distance drill to drill of 0.15mm. Or in other words: 0.25mm between the finished holes size diameters.

Why do we need this distance?

If the distance between the hole walls becomes smaller than 0.15 mm than this will result in bad drilling causing the base material to be damaged en drill bits to be broken. It results into an avoidable cost increase.

What is the smallest possible distance between non-plated through holes?

Between the non-plated through holes we also have to keep a 0.15 mm drill to drill distance. For NPTH holes the tool diameter is equal to the end size diameter Or in other words: we need 0.15mm between the finished holes size diameters.

Why do we need this distance?

The reason was explained under point B. above. If the distance between the hole walls becomes smaller than 0.15 mm than this will result in bad drilling causing the base material to be damaged en drill bits to be broken. It results into an avoidable cost increase.

Tolerances on PCB

What tolerances should I design into my PCB?

Where possible, design to PCB industry standard mid-range tolerances. If you use these tolerances you should be able to source your boards from any fabricator in the world without cost-penalty. Eurocircuits use these specifications and tolerances as the basis of our lowest-cost pooling services. Of course there may be times when component geometry or mechanical constraints mean that you need tighter tolerances. We can usually build boards to meet these requirements but they will cost a bit more as they need special handling or additional process steps (for example for blind or buried vias).

ACTION TIP.

It’s always a good idea to check your data-set and especially any drawings to make sure that they don’t specify tighter tolerances than you need. If they are outside our standard range, we may need to raise an exception, possibly delaying delivery and/or increasing costs.

NOTE

Minimum tracks, gaps and annular rings are defined in the specifications of each service and are not included in this table. There is a complete list in our PCB Design Guidelines p. 7.

Tolerances tables

Specification Tolerance Notes
Materials
Material thickness +/- 10% Based on manufacturers’ specifications
Maximum bow and twist on boards with SMDs 0.75% See http://www.eurocircuits.com/eurocircuits-printed-circuits-blog/bow-and-twist-in-printed-circuits
Maximum bow and twist on boards without SMDs 1.5%
Drilling
Production hole oversize – plated 0.10 mm

PCB Design Guidelines p. 8

Production hole oversize – non-plated 0.00 mm
Hole size tolerance – plated

+/- 0.10 mm

Hole size tolerance – via holes

+ 0.10/-0.30 mm

By default we take all holes 0.45 mm or less to be via holes. If you have component holes with finished diameter 0.45 mm or less, use the box in the Price Calculator marked “Holes <= may be reduced” to indicate the largest hole which can be treated as a via hole. The negative tolerance allows us to reduce via hole sizes to solve annular ring issues and/or to reduce board costs by reducing the number of drilling cycles needed. More.

Hole size tolerance – non-plated

+/- 0.05 mm

Aspect ratio 1:8 Ratio of board thickness to production drill tool
Hole positional tolerance 0.10 mm Hole to hole
Minimum hole to hole distance 0.25 mm Measured from production hole to production hole.

See PCB Design Guidelines p. 9 and technical blog

http://eurocircuits.com/eurocircuits-printed-circuits-blog/the-smallest-possible-distance-between-two-holes

Minimum non-plated production hole to copper 0.25 mm
Hole wall copper
Minimum copper thickness 20 μm
Surface finish thickness
Leadfree hot-air levelling 1 – 30 μm
Electroless gold over nickel Ni:3 -6 μm;

Au: 0.05 – 0.10 μm

Immersion silver thickness 0.2 – 0.4 μm
Plated hard gold over nickel Ni: 3 – 6 μm; Au: 1- 1.5 μm
Soldermask
Minimum soldermask to pad clearance = Mask Annular Ring (MAR) – plated holes 0.10 mm This depends on the copper pattern classification – see PCB Design Guidelines p.15
Minimum soldermask track cover = Mask Overlap Clearance (MOC) 0.10 mm On tight layouts there may need to be a “trade-off” between MAR and MOC – see PCB Design Guidelines p. 16
Minimum soldermask web = Mask Segment (MSM) 0.10 mm
Minimum soldermask to pad clearance = Mask Annular Ring (MAR) – non-plated holes 0.125 mm
Maximum tented finished via size 0.25 mm To ensure that the via hole is plugged with soldermask use ViaFill – see PCB Design Guidelines p. 16 & 20
Soldermask thickness on top of conductors >15 μm For more information see eC-Glossary.
Soldermask thickness on conductor edge >7 μm
Legend
Minimum line width 0.17 mm
Minimum height for legibility 1.00 mm
Legend to soldermask cut-back (clipping) 0.10 mm After clipping we also remove any bits of line smaller than 0.17 mm
Breakrouting
Minimum clearance board edge to copper tracks/pads – outer layers 0.25 mm Copper planes can extend to the board edge. Select “copper to board edge” in the Price Calculator
Minimum clearance board edge to copper tracks/pads – inner layers 0.40 mm
Minimum slot finished width 0.50 mm
Profile dimensional tolerance +/- 0.20 mm
Positional tolerance profile/cut-out to hole +/- 0.20 mm
Slot dimensional tolerance Width: +/- 0.10 mm

Length: +/- 0.20 mm

Minimum copper around plated and non-plated slots As annular ring for plated and non-plated holes
Scoring/V-cut
Maximum board thickness for scoring 2.00 mm
Minimum board thickness for scoring 0.80 mm
Minimum clearance board edge to copper pattern – outer and inner layers 0.45 mm This to allow for the V-cut. If copper pattern is nearer to the board edge, use breakrouting
Profile dimensional tolerance after separation 0.30 mm
Rest material 0.45 mm +/- 0.10 mm
Positional tolerance upper to lower score +/- 0.25 mm
Minimum score depth 0.15 mm
Edge bevelling
Nominal bevel angle 30° +/- 5° See eC-Glossary
Rest material 0.25 mm
ViaFill
Maximum ViaFill finished hole size 0.25 mm
Peelable Mask
See PCB Design Guidelines p. 19
Carbon
See PCB Design Guidelines p. 18
Heatsink Paste
See PCB Design Guidelines p. 21
Electrical Test
Minimum test pitch 0.10 mm
Smallest testable pad 0.05 mm
Test voltage up to 1000V
Test current 100 mA Adjustable
Continuity test Capacitance/

resistance 1 Ohm – 10 KOhm

Isolation test Capacitance/

resistance up to 10 GOhm

Marking editor

Adding custom markings – yet another PCB Visualizer function Do you need special text or a QR code on your PCB?  Or a production date code specific to this order? Or a logo that your design system can’t handle? Or is it important that order numbers and UL marking are in a particular location?  We […]