As a SEO expert, I frequently give advice to my clients to avoid using Frames based web design. There is no doubt that Frames make for bad SEO by causing website accessibility and usability problems. Even a well optimized web site design will struggle to achieve a high search engine ranking, compared to a non Frames web site design, even with proper use of the <NOFRAMES> tag for alternative content. For this reason when visitors reach the content Frame from organic search results they are left without any website navigation as the Frameset is not constructed properly. This is a website accessibility disaster and Frames prove little better for SEO either.
Frames can also cause search engines major troubles. For instance, a search engine may only deliver the content frame when accessed through deep links in the SERPs – thus rendering your well thought out navigation to other pages redundant.
Even though many search engine spiders today are able to read the content inside frames, the perspective of an SEO is that it is still a very bad idea for a couple of reasons. Frames are pages that consist of individual html pages that are put together in such a way that it appear to be one page. Frames were used by web designers to maintain a consistent and standard look among all the other pages on the website and for the purpose of navigation. The confusion for the search engines occur because they don’t reconcile the content in the frame with the page that the frame sits on – while the viewer may see the information as being together, the search engines may view it as a completely separate page.
One more reason it is a very bad idea to use frames is that some of the older browsers find it difficult or just plain impossible to read. Don’t take the chance of alienating visitors who don’t happen to have the latest software/hardware combinations.
Google Information about Frame based Websites in Google Webmaster Help Center
Frames can cause problems for search engines because they don’t correspond to the conceptual model of the web. In this model, one page displays only one URL. Pages that use frames or iframes display several URLs (one for each frame) within a single page. Google tries to associate framed content with the page containing the frames, but we don’t guarantee that we will.