You might wanna downgrade the driver cause I have the same card and this:
Lenovo ThinkPad E545
Network controller : Broadcom Corporation BCM43142 802.11b/g/n (rev 01)
If you are using this WIFI card, beware that bcmwf-kernel-source does perform very badly with a newer version
of the bcmwf-kernel-source 6.30.223.248-bdcom-0ubuntuXX (XX I have tried them all and all are crap)
Desripction of what is happening:
You are connnected to a network and when you are at signal level cca 55% and less the internet drops and you are offline for a long period of time (restarting card works for a few moments when the drop occurs again)
Solution: You want to downgrade to a bcmwf-kernel-source 6.30.223.141 (Lock it and don't update it)
+ To be sure I also downgrade linux-firmware from 1.127.12 to 1.127, just to be sure
Alternative solution: I have read a lots of lenovo users have this kind of a problem and it was DUE a unstable N module in the driver, so you might wanna disable N module of the new bcmwf. Look it up how to, I am OK with just downgrade.
Anyone from LINUX MINT TEAM please include a backport version of bcmwf-kernel-source 6.30.223.141 to a linux mint 17.2 :)
Possible WARNINGS: bcmwf-kernel-source 6.30.223.141 might not be included in Linux MINT 17.2 as the newer versions are believed to be working properly.