I selected my range of commits with shift + click, then the patch is created successfully, but i have a surprise when applying it. When i open the patch in editor, i can see that the first commit appears second, and also other commits are in wrong order. In my case, the first commit created a file and second commit edited the file created, so applying it in wrong order lead to a conflict (modification vs "deletion", since the file does not exist).

Since i dont want to solve those conflicts manually, and i don't want to edit manually the wrong ordered commits, i had to find a workaround to sourcetree "Create patch". Here is my workaround, using git bash : 

git format-patch 86d1e2a32f2d284c9f232082948452ed61b41351^..HEAD --output myPatch.patch

(and then to apply : git am myPatch.patch)