Intermediate CA certificates enhance the security of Digital Server Certificates. As of October 10, 2010, intermediates have been updated for Server and Code Signing products. The certificates are signed by an intermediate using a two-tier hierarchy (also known as trust chain or Chain of Trust) which enhances the security of your digital certificates.
Without the Installation of the intermediate certificate your server certificate may have trust issues on certain applications, although majority of browsers have the capability of fixing this on their own.
Note: If you have a pkcs7, p7b, p7s format SSL certificate the intermediate is embedded into its code, and downloading the Intermediate separately is not necessary.
Depending on your certificate brand you can download the intermediate CA’s from the below links.
If your server type also demands for the Root certificate to be installed along with your SSL and Intermediate certificates click Here.