Yes we have seen this type of issue before.

These are very difficult to assemble in reflow depending on the size and density of the board. One trick you may try is to reduce you top side temperature and increase bottom side heating. This will help keep the capacitor from getting as hot. You may also want to play with your convection air flow on the top side to reduce the heating.

You may be experiencing popcorning of your tantalum capacitors. We have observed this with several of our clients. Visually inspect and cross-section a random sample of caps post-reflow and see if you observe cracks. If yes, improve your storage conditions and the failures should go away.

My product is actually for selective soldering and not reflow soldering, but... recently I've been approached because of this same issue you are having. I will be doing a special application using a selective soldering machine to simply touch the bottom side of the board to a mini-wave and use it to reflow the solder on the top side. Of course the board has nothing on the bottom so there is nothing to interfere with it.

I don't know much about your actual process or another solution but I wanted to answer your question "Does somebody else see this problem". The answer is yes, other people see this problem. I hope there will be a better answer for you to correct this. But please contact me if I can help.

We have seen several situations where capacitors can fail if the internal core temperature of the cap goes above 150 ° - 180 °. The temperature is a function of the part itself and should be verified with the component vendor.

The key is the core temperature. So we recommend drilling a small hole in through the top of the capacitor and inserting a Thermocouple wire down into the core of the cap. Then seal it up with high temperature adhesive /epoxy. In this way you can properly measure the core temperature of the part and develop profiles accordingly.

In general, you can achieve profiles that will satisfy the solder joint temperatures of 235-240 and keep the body cool. In some cases, you may need to utilize differential temperatures between top and bottom heated zones. For example, when reflowing the cap on the top side of the board you can reduce the top side heater zone temperatures and increase the bottom side zone temperatures. The heat will conduct through the board and reflow the joints while the “cooler” air on the top helps to keep the capacitor body within spec.

Your oven supplier can work with you on the details. The best thing to do is provide the oven supplier with the profiles you are running now and the parameters you need to meet and they can typically provide guidance on changes to zone temperature and process.

But it would be best to get that capacitor outfitted with a T/C first and then run it through so the oven vendor can have that baseline info from which to operate.