Solder alloy leaks into vias on pad/pads, through hole. What to do?
Author Dmitrii Khramtsov
November 19 2024
Introduction about developing PCBs problems.
From my work experience, I can confidently say that more than half of the printed circuit boards received for assembly from different companies have defects associated with open vias on pads and through hole problem.
Why is there a printed circuit board with such actions? Maybe the developer’s experience is not enough, maybe there is no desire to develop electronics correctly, maybe speed of development was needed, or maybe the proverbial chance. I don't know.
Problem: The open via is inside or very close to the pad polygon. When soldering, the solder begins to flow into the hole, exposing the connection.
- At the same time, the quality of soldering leaves much to be desired.
- Only that part of the solder that is attracted due to the capillary effect remains soldered to the contact.
- There are no solder fillets on the contact pad at all.
- The connection does not pass through any of the IPC standard classes.
- The connection does not follow the IPC standard.
- Also, having solder on one side of a component and no solder on the other side often creates a tombstone effect - the side of the component with more solder lifts the component.
- Or 100% shifts the component to the side where there is more solder, which is also a defect.
How to fix design mistakes when solder leaking through an open hole?
1) Covering the transition hole if it is near the site, but not inside the site. In general, metallization layer - tenting is a good practice in the development of printed circuit boards so that neither flux nor solder gets into the via hole.
2) Move any vias from sites, except for earthen and other large polygons. I know and confirm that there is always an option to re-route the printed circuit board in such a way that the via hole can be moved out of the pad to the side. Even in BGA and FPGA conditions. It's a matter of qualifications or desire.
3) If there is really no way to get rid of the hole in the pad, then you can create a via hole in the contact pad and cover it with a metallization layer similar to the pad itself. In this case, the hole will be filled with a conductive or non-conductive compound so that there are no voids left inside the hole.
Remember the main thing - almost any mistake or defect of the developer is corrected by the hands of the assemblers and you will then be presented with an invoice for payment for this work. Therefore, it is always cheaper to invest money in redeveloping a printed circuit board than to pay for repairs of the same printed circuit boards in manufactory. What if these are tens of thousands of boards?
Let's summarize
Of course, when soldering printed circuit boards and repairing them, it is necessary to use high-quality soldering flux, which can be easily washed if necessary, and which does not conduct electricity and does not create leaks between the conductors of printed circuit boards. Moreover, unwashed residues of high-quality soldering flux will not cause corrosion on the printed circuit board and conductors. I recommend using a quality river flux such as
Soldering Gel Paste Diamond Flux FN231 and
Liquid soldering Diamond Flux FN232. Stores for each soldering flux are listed on the main page of this site. You can also read other articles on this site.
Thank you for reading this article about improperly created vias on PCBs.