I have two different Qi charger pads and two S5 phones that both have the same Spec CandyShell case on them.
Both of the phones are ticklish about being placed on the charger pad in "just the right place" to get the wireless charger going.
Both w/o the case will instantly start charging and aren't so picky about being placed correctly.
I have discovered on both of my pads, the "correct way" is for the pad cable to be at the "rear side" and the S5 top to be towards the pad's cable.
I have also discovered that placing the S5 over the pad, sliding it down towards the non-cable end and then slide it back up towards the cable end will cause it to start charging immediately.
It takes a bit of practice to discover how your case and charger pad combo work together.
The issue is, the case adds "space between" the phone and the charger pad. This reduces the field intensity of the charging pad's transmitter to the phone's wireless receiver coil.
These things are sold at $10-20 bucks, and don't have any extra power to be sloppy about phone placement with a case on the phone.
No case? not so bad, charges "now" as long as it is on the pad.