Here is the tool from which you can check yahoo back links http://www.searchenginegenie.com/yahoo-back-link-checking.html
www.backlinkwatch.com is a really nice tool to check backlink with lot of details. this is a nice site, easy to use and easy to remember. or you can use yahoo site explorer.
Just type this syntax at yahoo search bar: link:www.yourdomain.com Very simple, isn't? However, it only show result up to 10K backlinks.
The best is to use siteexplorer.search.yahoo.com - Yahoo Site Explorer tool. It can provide you all the backlinks for your site.
as people said sign up for webmaster account in yahoo and you willl get all the information you will need.
There is a Tool called SEOQUAKE install it in your browser any its show back link of different search engines, it also provides a lot useful options for major search engine including yahoo.
you can be check the yahoo baclinks by applying the query on the yahoo explorer that shows all the back links that is links:url of the site then search now you can search the backlinks except to your domain or other what you want
Use siteexplorer.search.yahoo.com And check your website. Please also note, that there can be huge difference between www .domain.com & domain.com - so i recommend you to check both variants
Go to Yahoo.com and click inside the search bar. In the search bar you need to type in site:www.yourdomainname.com, replacing the sample domain name with your own of course. Then hit enter or click on "Web Search". This will take you to a page in Yahoo! called the Yahoo! Search Site Explorer. or http://www.searchenginegenie.com/yahoo-back-link-checking.html Code (markup):
you can check the yahoo link by simply right the query on the yahoo site explorer link:url of the site for which you want to see the links