Keepout region for Molex SMD connector footprint

Question

I am trying to understand the technical justification to have a keepout region around the 2 large outer pads of a Molex connector (PN# 5055670881).

I would like to have more area around these outer shield pads to add some vias for strengthening the vertical connection through the board structure.

One other thread on the internet mentioned something about a ‘solder keepout layer within a trace for a connector’ to help with pulling the connector down flat to the board. I am not sure that is the same reasoning for this type of connector because the KO region is in a totally different area…

Any insight would be great!

Answer 1

It's because that's where the plastic housing of the connector sits on the PCB. Of course, you wouldn't want to place any other components within the overall outline of the connector, though some people might squeeze an 0201 resistor in there. But, specifically, you cannot place any components in the keepout areas because they would keep the connector from reaching the PCB.

Answer 2

I guess, the manufacturer just wants you to watch out for areas of your PCB that are touching the housing of the connector (see the orange surfaces in the STEP model below).

The datasheet says: "Pattern is not recommended on the hatching area" (referring to copper structures in those "keep outs", I guess). Maybe it's not really a "keep out" per se. It might be more like "Better not have anything in those areas. But if you do, make sure it's not a problem."

I have no experience with this connector. But I don't see why vias should be an issue here. However, manufacturers usually don't pull such recommendations out of thin air. Often times a customer or the manufacturer himself (during testing) had an actual issue.

An uneven surface could prevent the part from moving in its place during reflow (surface tension of the melted solder). Or copper structures might lift the component slightly and compromise the solder joint.

But the rational behind this recommendation isn't obvious to me, either.

Maybe you can ask Molex directly.