From the moment of publication (see Art. 32 Spanish Patent Law 11/1986 March, 20, SPL from now on) of the application in the Spanish Official Gazette you can choose two different procedures to continue with your patent application prosecution:
First one, in which within three months following the date of publication referred above, a request can be filed for examination of the sufficiency of the description, novelty and inventive step of the object of the application (substantive examination). In the event of not wishing to file a request for examination, this could be notified to the Patent Office irrevocably in writing, within the mentioned three-month term although, in the absence of notification by the applicant of his wish not to request examination, publication of resumption of the general grant procedure will occur upon elapse of the mentioned three-month term (see Arts. 32-38 SPL).
Second one, if the applicant decided to file a Request for Examination, the steps above would not be of application, but rather the steps relating to the grant procedure with prior examination would come into play (see Art. 39 SPL). Once the request for examination is published, the Patent Office will examine the patentability of the invention an shall, if the result of such examination favors patentability and there have been no oppositions, proceed to grant the patent application (see Art. 39.7 SPL).
As you can see, pursuant to Spanish Patent law, request for substantive examination is not compulsory. Even more, and surprisingly, is not usual to request it and the application can be allowed without substantive examination and even with a negative search report but, indeed, the patent allowed can be more easily challenged in court.
Spanish Patent Law