品牌 vs 牌子

I want to know the difference between 品牌 vs 牌子 in terms of usage. Please don't answer this here, but answer it at this link instead. If the question is answered at this link, then it will be posted in the glossary for these terms. thanks. http://chinesepod.com/tools/glossary/discussion/%E5%93%81%E7%89%8C