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Please note that all names used are completely fictitious and any thing written is my own personal opinion or knowledge and not related in any way to either my employers or their customers (or Zuken).
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Tuesday, 14 January 2014

Adding teardrops to PTH pads in P.R.Editor.

Pad with broken track
Pad with broken track
When you have a component such as a terminal block with PTH pads that are likely to move during use (i.e. when tightening the terminals) the pad can rock and if that pad has a thin track exiting it there is a potential for the track to break at the junction with the pad as shown
(slightly exaggerated) on the right.

This problem is prevented by exiting the pad with a thicker and slowly reducing to the width of the track piece of copper, this copper item is referred to as a teardrop (due to its shape).

Pad with teardrop
Pad with teardrop
Adding teardrops to pads is something that requires the user to consider which pads require a teardrop, what size it should be etc. As such it is not something that the auto router will do for you, instead it is a manual operation.

Given that teardrop use is currently not required as much now that the majority of components are SMT, manually adding them is not really an arduous task.

Personally I have only ever used teardrops by manually adding them within the CADSTAR Design Editor, it only takes a little time and is easy to do, however there are functions to allow you to automatically add a teardrop to a pad when manual routing in the route editors.

This does however require some setup in the PCB from within the Design Editor before you can use them in the router and here is how I have found best that they can be added.

It is important to note that teardrops are added on a per pad code basis, what this means is that every pad code that uses them needs to be setup individually before the router can add a teardrop to a pad.

Identify the pads that need teardrops, if there are only a few then simply route them in the router and return to the Design Editor to add them, note that it requires the route to directly exit the pad (without route offsets or doglegged tracks) then choose the track properties where you can select either teardrop at the start or finish end of the track. Assuming that there is room to add it and that the track exits correctly then it will be added.

Adding the teardrop to the route properties
Adding the teardrop to the route properties

Router Auto Teardrop feature.

There is an auto-teardrop function in P.R.Editor that adds a teardrop to the pads during manual routing.
You first need to add a teardrop to at least 1 pad of each pad code requiring teardrops before entering the router to add the rest of them during manual routing.

What this does is it adds the attribute information to that pad code so that you can enable the auto teardrop function in P.R.Editor (this setting is not available within the embedded router) so that when manual routing out of further pads of the same pad code teardrops will be automatically added.

There are further changes that you can make to the pad codes within P.R.Editor that allow you to add teardrops to other pad codes etc.

Within P.R.Editor if you go to Configure\Attributes and the teardrop tab you will see a list of teardrop names with additional fields for teardrop angle, length, offset, style and width. These can be adjusted to suit.
These teardrop rules are named TDO, TD1 etc.

Teardrop name setting in P.R.Editor Attribute Editor.

Also on the Pad Code tab there is a column for the above teardrop rule to be used on each pad code, by selecting the field you can select the teardrop rule to use per layer or as the default.

Selecting the default will cover all layers however you can have different rules per layer or perhaps only on specific layers.

You can copy/paste a rule to other pad codes that do not have a teardrop on already.
Teardrop per pad code setting in P.R.Editor Attribute Editor.
Teardrop per pad code setting in P.R.Editor Attribute Editor.

Routing Setup Option.
Routing Setup Option.
Once this is all setup then turning on the feature in the routing
setup and manually routing the board will automatically include teardrops on the pad codes that have them set.

A slight drawback is that this applies to all use of that pad code so
if there are several pads that do not want teardrops on then simply
turn off the function.

A point to note is that the attributes used to setup the teardrop rules do not appear in the Design Editor Attribute Editor lists of attributes for you to modify, they are only available within P.R.Editor. Also the feature works in the embedded router as long as it is first enabled in P.R.Editor.

Some additional information on teardrops:
  • The Defaults\Routes tab contains the default angle setting.
  • In the Design Editor when in select mode you can grab and adjust the teardrop to extend or shorten it.
  • The colour of teardrops can be found in Colours\highlights.
  • There is no point adding teardrops to SMT pads that are not used by connectors.
  • There is no point adding them to large vias.

Routed teardrop.
Routed teardrop.

An alternative suggestion:

I have an alternative suggestion to all the above, when manual routing
simply exit the pad using a large typed width for a short distance and then revert to your normal routing width.

This is simple to do and can be done without any additional setup
(Ensuring that the route code has a large enough max width set).
Looks odd - but it achieves the desired results.


Anonymous said...


Anonymous said...

Thanks a lot :)

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