Art. 19(2) EPC stipulates that an opposition division must consist of three technical examiners, at least two of whom must not have taken part in the proceedings for grant of the patent to which the opposition relates. An examiner who has taken part in the proceedings for grant of the patent may not be chairman of the opposition division.
Source: http://www.epo.org/law-practice/legal-texts/html/caselaw/2019/e/clr_iii_k_1_3.htm
Date retrieved: 17 May 2021