Is it really the bobbin thread that is globbing? Check closely. Usually it is the upper thread accumulating under the fabric.
If it is in fact the bobbin thread, then the bobbin case is not threaded correctly, the bobbin case tension needs adjustment, or it is broken and needs replacement. There are web sites and YouTube videos that show how to adjust the bobbin case tension.
QUICK FIXES: Remove all the thread from the machine. Clean the area around the feed dogs and bobbin area. Oil as instructed in the owner's manual using ONLY fresh, good quality sewing machine oil (only 1-2 drops each spot). Install a brand new needle insuring it is installed correctly. Avoid using fuzzy, old, or bargain bin thread. Rethread: Be sure you raise the presser foot BEFORE threading the upper thread so it will seat properly in the tension disk--and check to make sure you are threading the machine correctly. Check that the upper tension is set properly (the factory standard is usually the halfway point between the high & low number on the selection). Test on a scrap of the fabric you wish to sew. Adjust the upper tension--either tighten to pull the upper thread toward the top of the fabric, or loosen to pull more upper thread down.
Here are some web sites that may help. Sewing Machine Thread Bunching Up Here Why sewing machine birdnesting https://answers.yahoo.com/question/index?qid=20100303212248AAnRUQA 8 Tips to Fix Birdnesting in Embroidery Birds nest under the fabric big loops of thread top side looks good...
and here's another Hint that may be helpful: