Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE chip_model (model_name VARCHAR, chip_model VARCHAR, Accreditation_type VARCHAR)
TABLE: CREATE TABLE phone (model_name VARCHAR, chip_model VARCHAR, Accreditation_type VARCHAR)

### Question ###
Find the names of the chip models that are not used by any phone with full accreditation type.

### Accurate SQL ###

SELECT model_name FROM chip_model EXCEPT SELECT chip_model FROM phone WHERE Accreditation_type = 'Full'