Next week at f8, Facebook will unveil Facebook Audience Network, its mobile ad network that will let developers target both standard banners and custom ad units with Facebook’s vast trove of personal data, according to multiple sources. It could let developers monetize, advertisers buy more mobile impressions than News Feed can fit, and Facebook earn money without cluttering its own apps with more ads. Facebook began testing a mobile ad network in 2012. Because it was just a targeting layer on top of existing ad networks that it had to split revenue with, margins weren’t high enough so Facebook paused it to focus on its native monetization efforts. Then in September 2013 it announced it was rebooting mobile ad network tests and this time it would work directly with advertisers and publishers (apps that host the ads) which would let it keep more of the bounty.