How to trigger sass build after mix.copy is completely executed using Laravel-Mix

I have implemented Laravel-Mix in my application and copying files from node_module to my assets folder and than compiling my scss. Since the copying process is slow my scss is not able to find the dependent libraries. Is there a way to delay the sass build and trigger it after copying task has completed?

Here is my webpack

 let mix = require('laravel-mix');    
 mix.copy('node_modules/ionicons', 'resources/assets/css/libs/ionicons')
 mix.sass('resources/assets/css/sass/app.scss', 'public/dist');

Below is my app.scss

@import '../libs/ionicons/dist/css/ionicons';
@import 'header';

Here is the error I am getting

95% emitting ERROR  Failed to compile with 2 errors7:38:04 PM

 error  in ./resources/assets/css/sass/app.scss

Module build failed:
@import '../libs/ionicons/dist/css/ionicons';
^
      File to import not found or unreadable: ../libs/ionicons/dist/css/ionicons.

via Chebli Mohamed