ram causes bluescreen in partners laptop

Tried to upgrade my partners laptop a while back, after opening it up we learned one stick was directly soldered to the board with a slot next to it for one stick, i made sure clock speed and everything matched the existing ram, the computer would bluescreen consistantly every few hours so i took it out and used it on my laptop instead, it worked perfectly in mine and ive not had a bluescreen on my laptop for any reason, any ideas on why its causing problems in their laptop specifically? They run a windows 10 system on a lenovo laptop that was purchased new