Insufficient hole filling and why?
There are many many reasons for this and I would not know where to begin, but a more information would have been useful, such as board thickness, finished hole size, board plating material, flux type and flux application method and finally the type of solder being used in the wave solder machine, is it lead-free or leaded solder?
Not knowing any of these items, check the following:
- Flux application and its penetration through the board,
- Top side board temperature going into the wave or coming off the preheaters, is it high enough to allow the molten solder to rise through the board.
- Depth of the board in the wave, try running the board at least 1/2 of the board thickness in the wave to use the hydrostatic pressure of the wave to push the solder up into the plated through hole.
The second item is voids in the solder joint.
This can also be caused by a variety of reasons and the primary one which comes to mind is bad plated through hole barrels. Check the plating in the barrels to make sure there are no voids. See IPC-600 for the criteria. Voids will have a tendency to create outgassing and this creates voids in the solder joints.
The other issue which could be causing this is if VOC free fluxes are used and the application is putting on too much flux and it is not drying off during the preheat stage of the wave solder system. As this product hits the wave solder system, the liquid will volatize and this will also create voids and blow holes in the solder joints.
I hope this helps, if more information is needed please get in touch with me.