1."It is always not necessary**, however**, we use it to link two parts of that instrument".

‘However’ can be used to join two simple sentences to make a compound sentence. But in (1) there is a mistake while using the punctuation, that is "however" and the comma after "necesssary".This is corrected by using semicolon and comma like this "It is always not necessary; however, we use it to link two parts of that instrument".This is OK to me, and here no doubt to me.

2."It is always not necessary, however, when we use it to link two parts of that instrument".

I think there are to mistakes here one is by using comma before necessary and other is after conjuctive adverb a subordinate clause is used. Here is my question. Can we use a subordinate conjunction after the conjunctive adverb?