Software architecture deals with the abstraction part of design, it analyzes the problem and sets a methodolgy to solve it, commonly using blocks. The software architect must be very acquainted with the challenge that he is facing, along with the technologies that can be used to solve it. Nonetheless, the SA doesn't do coding, he gives the product owner a thorough analysis and the underlying structure of the program that must be made, including a design blueprint and the attributes and connections of each part that has to be implemented later.
Software Architecture is, in essence, delivering a structured solution to a problem.
Software Design, on the other hand, deals with the technical details of the implementation of the system. They take into account the environment, adapting the development process to it, incluiding software and hardware constraints. They design and guide the coding process, including testing and debugging, in order for the process to be orderly and ensure success.
Software Design creates the functional part of the archutecture plan.