is you bobbin thread catching with the top threads. No reason for the seams to come undone. Do you backstitch? If you don't do you perhaps clip the threads too short before attaching to the other rows/pieces?

If not, then I have to agree with the others

Sewing at 1/2 inch isn't going to be any better then at 1/4. If it's coming apart it will come apart, no matter how big your seam

The only time my stitching comes apart is when I didn't keep the seams straight so the rows slip apart and I've learned to backstitch at the beginning & end of my rows before starting the final assembly into a quilt.

Chain piecing with no little tail left between the patches will also quickly unravel. My machine doesn't like the couple empty stitches between the patches so I've just quit trying to do it that way.

I would definitely change the way you are doing something else before changing all my patterns to 1/2 inch seams. Fabric is too expensive to eat up with seams.

Flannel can also be sewn with 1/4 seam allowances without fear of it coming apart if it is prewashed, pressed with a very hot iron and you are very consistent with your 1/4 inch. The prewashing, drying and pressing should shrink/draw it up enough to hold even the looser weaved (usually cheaper but not always) flannel together. Less than 1/4 inch anywhere in the seams and it will unravel enough to reach into the seam line and come undone.

Another idea is, Are you pressing your seams open? If your tension is loose and you are pressing your seams open, that could easily weaken the thread enough to pop seams.

Post a photo of the back & front sides of one of your finished blocks after you have pressed them so we can see what's going on.

Thank you all for your input. I am using a Babylock machine and my stitch length is 2.5. I will attempt your suggestions and will try and use a smaller stitch length. Must I also stitch in the ditch on the quilt top to set the seams? Again, thanks to all. Laura A in Brick, NJ

No, you don't have to. The seams should be stable on their own before you get to the quilting. So FMQ to your heart's content. And you should see the difference in the unquilted top.

Now, don't go making the stitch so small you can't "unsew" it if needed. I have no idea what a 2.5 means on a Babylock. I sew on a 2.2-ish on my Bernina.

Let us know how the smaller stitch works out for you.

My mother always used a seam greater than 1/4", the end result was simply a smaller block. I never could get her to go to a smaller seam. Doesn't solve anything for you unless you are willing to have smaller blocks and work with that. She always said she felt more comfortable with the larger seams.

Is it the thread that is breaking? Is it the fabric coming out of the seam? I would first look at the thread, then the stitch length. I piece with my machine set at 2.0 and have not had seams come apart. I do chain piece, sometimes with leaders and enders. I also strip piece, so backstitching at the beginning and end would not help. Also, quilts that are tacked or tied have more stress on the seams, during use and washing, than a quilt that is machine quilted all over.