Defect of the Month – Tombstoning of Chip Components
Hello, my name’s Bob Willis and welcome to Defect of the Month. Every month, I try and provide an example of a particular defect and hopefully some solutions. I’ve made over a hundred different defect videos over the years, so hopefully one will solve one of your process problems.
A common process defect that we see quite often in manufacturer is the tombstoning of chip components. Now here’s a couple of examples. The first I show the lifting of a component during reflow soldering that we would traditionally refer to as tombstone.
In the second example, you can see the same effect taking place, but in this particular situation, the component only partly lifts, which on some AOI inspection systems may not be spotted. Now tombstone predominantly is affected by the process, the design, and these are some of the reasons why you might see it in manufacture. Now the pad size for chip components has to be right. If we’ve got uneven pad distribution, or sometimes the pad separation distance based on the termination of the components, this can contribute to lifting. If you’ve got some other interconnection to one side of the passive component, again, it may significantly affect the time of reflow and where you get. Reflow not happening simultaneously on each termination. This can be a contributing factor. Probably one of the biggest contributing factors to tombstone is the volume of solar and progressively as we started to use less and less solar paced in terms of thickness on the surface of smaller and smaller parts and boards, we’ve generally seen less tombstone take place.
If you’ve got solar pace, that’s got poor T qualities. We may find that during the placement, the component is not held in place sufficiently, possibly on one end. And this may be the reason why, even if we’ve got simultaneous reflow on both terminations, the part may lift anything underneath the component, which can generate movement. So if we’ve got solar paste due to slumping underneath the part that comp reaction may be the root cause. Why a component lifts during reflow because there’s energy underneath the part, as the part moves into the reflow process. And the wedding starts
To occur on the terminations solar mask underneath the component can vary in thickness. And if there are copper traces underneath the solar mask, again, that affects the thickness of the mask. So we get a Seasaw effect which can occur. And certainly I’ve seen this in manufacture. When you go below oh 4 0 2, you really don’t need solar masks between the terminations. You are probably less likely to actually have copper between those terminations of the passive part. So again, why have the solar mask there in the first place you will generally find if you compare convection reflow with vapor phase or convection, reflow in nitrogen that with nitrogen and vapor phase, with a poor design, you are more likely to see tombstoning occurring on boards. So we’ve got to think of ways of significantly improving the process. One of the simple tricks that I’ve used many times with convection in nitrogen is reduce the nitrogen content.
You’re slowing down the wedding characteristics. You are saving money, but more importantly, in a short term, you’re reducing the lifting of the part, which is a key issue. We’ve also seen sold ability play a part. If we’ve got variations, inability between each termination, even if every other aspect of the reflow process is perfect. You might necessary, you might see the component tends to wet to one termination quicker than another. Hence that lifting occurring. Thank you very much for listening to defect of the month. Hopefully it’s been useful and possibly you found a solution to one of your process problems. So just a reminder that if you want to listen to more defect of the month, subscribe to our channel, if you just like this individual video, then please like it. And of course share it with some of your colleagues in manufacture and in other companies, it all helps to bring information to both production and engineering staff. If this short introduction to this particular problem was of interest to you, then of course we can hopefully provide you a solution to aid. You eliminate more process defects within the future.
