How can the formal charge of the B in the Lewis structure of BF4(-) ion be minus one?


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> How can the formal charge of the $\ce{B}$ in the lewis structure of
>  $\ce{BF4-}$ ion be minus one ?
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I draw the lewis structure of $\ce{BF4-}$ ion such like the following:
I put $\ce{B}$ in the central position and make single bonds between $\ce{B}$ and $\ce{F}$s, then completed the octet of $\ce{F}$s.


But in such a structure, the formal charge of $\ce{B}$ is $-1$, and the FC of $\ce{F}$s is 0.However, we know that if someone is going to get a minus FC, it should be the one whose electronegativity is the highest, and in this example this rule is not followed, so what is the reason for that ?


