Yin shot a seven-under-par 64 on Friday, leaving her at 10 under and level with Kim who carded her second consecutive 66.
Defending champion Nasa Hataoka (66) of Japan sits alone in third place at nine under, while Canada's Maude-Aimee Leblanc produced her second straight 67 for fourth place at eight under.
Hannah Green (67) is the best-placed Australian in a tie for 12th at four under. Sarah Kemp (67) is one shot back, while Grace Kim (71) is even the card and Steph Kyriacou (69) two over.
Yin completed a symmetrical round: four birdies on the back nine, then her lone bogey at the par-4 18th hole, then four birdies on the front nine.
The 20-year-old, in her second LPGA year, is trying to top her career-best result of a tie for fourth in Ohio last September.
"Today I played pretty good," Yin said.
"I think I hit 13 fairways and 13 greens and 24 putts, which is amazing for me I think ...
"I felt my game was in a pretty solid spot right now. I can strike the ball well and my approach shots (are) pretty good. Yeah, everything is pretty good."
Kim's error-free day included consecutive birdies at Nos. 6 and 7 as she finished on the front nine.
"My short game today was really good and I think that led to a bogey-free round," Kim said.
 "There were a couple situations actually where I could have carded a bogey, but in those instances my putter worked well."
Hataoka also completed the second round without a bogey, capped by a birdie on the par-4 ninth.
"The plan for today was simple: Do the same thing I did yesterday, try to focus on my shot, try not to think too much about my shot, and I think that really worked out today," Hataoka said.
First-round leader Mi Hyang Lee of South Korea stumbled to a 74 on Friday and is tied for 16th at three under.
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