Dear Khun Sirirat ,
please provide the document as the attached leaflet.
http://www.bangkok.diplo.de/Vertretung/bangkok/th/08/Besuchsvisum.html
for the further Information please visit our website www.bangkok.diplo.de
Your boyfriend has to contact the immigration bureau in Germany directly, whether he can use the personal identity card or not.
Best regards,
Visa Section