Confidence among big Japanese manufacturers likely improved slightly in the three months to June, while non-manufacturers' mood slipped a bit, the Bank of Japan's (BOJ) closely-watched tankan survey is expected to show, according to a Reuters poll of 18 economists. The tankan manufacturers' sentiment index likely stood at plus 12 in the June quarter versus plus 11 in the prior three months, with their confidence improving further to plus 13 over the coming three months.