This is a good question. I'll try to answer as briefly as I can. There are basically 3 types of lower back injuries associated with Squats, especially with loads.
#1. But wink: This mistake occurs when you go down on your squat with your pelvis tilting while your tailbone kinda tucks under you butt. This can cause lower back injury with spinal disc injuries quite a common occurrence.
Solition: Keep your pelvis neutral when squatting. Make sure you have good ankle mobility, as your knees tend to move much better with good ankle mobility. Having tight ankles will disrupt your center of gravity forcing your body to compensate by leaning back and hurting your lower back in too he process.
#2. Hips rising faster than your chest: When ascending from a squat, your hips and chest should rise at about the same rate. This prevents your body from compensating by shooting your hips backwards, as your glutes + lower back carries the load which could eventually result in lower back injuries. Your ascent must be smooth without your hips shooting backwards. You should check your weights as well.
#3. Breathing: Typically, you breathe in when descending in a squat and breathe out when ascending. However, when doing a squat with a heavy load, this technique may a use instability during the squat leading to a high risk of injuries. There's a technique called IAP (Intra-abdominal Pressure) which will help to stabilize your back, reduce lumbar load, and spinal pressure. You need to imagine yourself going underwater on this one. So you take a deep breath, hold the breath, and firm up your core before you descend in your squat. As you ascend you can then exhale, then reset for the rep.
I hope this helps, stay safe.