BGA neckdown clearance issue

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1

Hello,

I am observing an interesting clearance violation when adding BGA neckdowns.

The image below shows a clearance violation at the point where the trace width expands to the default width.
It only shows up when doing a neckdown between BGA pads. The default trace width is 0.1mm and the neckdown trace width is 0.08mm. The default clearance is 0.1mm outside of the BGA, and 0.075mm within the BGA. The BGA pitch is 0.5mm.

neckdown-clearance
neckdown-clearance1630Ɨ1292 98.7 KB

Interestingly, this issue does not happen when there is no neckdown and the default trace width is used, shown below.

no-neckdown-clearance
no-neckdown-clearance1168Ɨ1225 84.7 KB

Iā€™m interested to know what might be happening here. It seems like it is either a setup issue or a bug. Iā€™m using KiCAD version 7.0.5.

Thanks in advance!

2

Hi @Bren

It is probably worth upgrading to 7.0.7 before trying to chase down the problem. There have been a lot of bug fixes since 7.0.5.

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That exact example is very difficult to replicate and even then it may be fruitless. You didnā€™t even tell how you implement clearance rules for default/ā€œwithing the BGAā€. You should attach an example project, either that one or something which just shows the problem.

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This could be issue Cannot route track close to another track with two segments of different widths. (#15311) Ā· Issues Ā· KiCad / KiCad Source Code / kicad Ā· GitLab.

The width-change is common to your description and to the bugreport.

2 Likes
5

Hi Maik,

Thanks for pointing out bug #15311.

This is is exactly the issue I am seeing. Iā€™ve added a comment to the bug with the version info - if this helps at all.

For a temporary workaround I will enable ā€˜Allow DRC violationsā€™ in order to break out this BGA.

Thanks again!

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