دلیلimplode نشدن در php

$ch1 = curl_init();
        curl_setopt($ch1, CURLOPT_URL,"https://www.aparat.com/v/IknZ2");
        curl_setopt($ch1, CURLOPT_FOLLOWLOCATION, 1);
        curl_setopt($ch1, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch1, CURLOPT_ENCODING, 'UTF-8');
        $cc = curl_exec($ch1);
        curl_close($ch1);
        echo $cc;
        preg_match_all("/<h1 class=\"vone__title\">[\W\w]*?<\/h1>/im", $cc,$f);
        $yy=implode(",", $f);
        echo $yy;

چرا نمیشه implode کرد و این ارور رو میده
Array to string conversion in