Gold Plated vs Nickel Plated SMA connectors

Hello,

I am using high frequency (6GHz-8GHz rated) SMA connectors in my new design, and Digikey has exactly what I needed for 1.0mm PCB, but here is the thing - they have two suitable connectors manufactured by Taolgas and while they look the same from spec stand point, body finishing is different - one is gold finish (gold color) and another is nickel finish (silver color). I somehow liked silver oned because they do match enclosure color, and were a few cents cheaper. BUT, here is the thing - I have really, really hard time to solder them to PCB pads (not the RF pin, which is gold, but ground pins on top and the bottom). I already tried everything - different solder materials, different flux mixtures, different soldering irons, different temperatures etc. - nothing helps, solder just does not "stick" to the body. The same exact SMA model with gold finish solders like a charm.

Any ideas? Any experience with this kind of finishing (nickel)? I already tried to contact manufacturer a few times, but the best answer that I got so far is "Can you please describe us your project?" - looks like one way communication. I do recall now having similar issue with another connector about a year ago - didn't bather, just threw them to garbage can and settled on gold ones.

Does anybody ever had similar experience with nickel finished RF connectors?

Yes, I had such experience few years ago. I ended up using steel soldering flux:
1) put few drops of flux in plastic cap from used bottle
2) soak soldering part of each connector and put on the tray
3) right before soldering clean each connector with alcohol pad
4) solder with pretty high temperature, maybe 300°C, depends on board metallization and soldering iron performance
This way it soldered much better, but still could not get it perfect.
Flux layer in the cap was very thin, around 0.3mm, to reduce chances it will contaminate connector internal part.
I was able to solder it very well when used more of this steel flux, but worried about corrosion. Do not remember exactly what kind of flux this was, it had "steel" or "stainless steel" on the sticker.
If there is only a few connectors to solder, I just try to use such steel flux in a more complicated manner:
1) put a lot of flux on soldering parts
2) put some solder without connecting to the board. Need good ventilation, because flux will evaporate
3) use soldering wire to remove excess of solder, probably most of it so connector could be fitted to PCB
4) maybe clean it a little after it cools down
5) finally solder it to the pcb as usual

Most (if not all) the Nickel plated SMAs are made from brass.
I made once the mistake using these connectors.
The only way to solder them was scratching with a sharp knife the plated Nickel from the zones need to be solder.
Is not very easy to remove the Nickel, and perheaps not very professional , but soldering directly on the brass body will work right away.
Solder the zones of the SMA before placing the connector on the PCB. In this way the final soldering will be done much faster.

Agreed, soldering to the nickel plating is a horrible experience, while soldering to the gold is not problem. My understanding is that the gold plated connectors also run to a higher frequency (18 rather than 12 GHz), due to the losses in the nickel coating.