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I'm designing a circuit requiring MMCX board edge connectors, specifically using the Molex 73415-0961 jack. When looking through the datasheet for suggested PCB layout, I see mention of an additional optional feature. But there's no mention of purpose for this option and I'm curious what it's designed for.

Here's a screenshot of the layout with the optional feature highlighted: Molex 73415-0961 PCB layout with optional feature

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  • \$\begingroup\$ What is your question? please edit your question and provide a question. \$\endgroup\$
    – Voltage Spike
    Apr 1, 2016 at 23:29
  • \$\begingroup\$ @laptop2d I think "What's it for?" works. Am I missing something? \$\endgroup\$
    – bitsmack
    Apr 1, 2016 at 23:33

2 Answers 2

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That is a rectangular piece of soldermask used as a "solder dam". It is used in cases where the microstrip ("rf trace") doesn't have a soldermask coating.

During assembly, solder paste is applied to the exposed pads under the connector. But if the microstrip isn't covered with soldermask then the solder will flow along the microstrip. This makes for a bad solder joint, and also will change the characteristic impedance of the microstrip.

The solder dam simply acts as a barrier to keep the solder where it belongs.

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  • \$\begingroup\$ @KjonVALIS Glad to help! While I appreciate your accepting my answer, it is usually suggested to wait for a few hours or days to make sure a better answer doesn't come along. Of course, it's pretty unlikely in this case! :-) Ha! \$\endgroup\$
    – bitsmack
    Apr 1, 2016 at 23:30
  • \$\begingroup\$ Ah.. suggestion accepted. Will do in the future. \$\endgroup\$
    – Kjon VALIS
    Apr 1, 2016 at 23:46
  • \$\begingroup\$ @KjonVALIS Have a nice weekend :) \$\endgroup\$
    – bitsmack
    Apr 1, 2016 at 23:50
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I would have guessed it is a stub. This is not quite the same configuration, but I just modelled the same connection on CPW with Rogers 4350 and no matter what I tried, I was always left with at least 5j ohms of reactance. Adding a stub as shown here got me down to a (theoretical) VSWR of less than 2%.

enter image description here

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