Question about capacitors

一沙一世

Question about capacitors [Copy link]

 

I have used chip capacitors (connected between the 3V power supply and the ground) in a product powered by a 3V lithium battery. I have found that occasionally (with a probability of one percent) the resistance value is only a few hundred ohms or they are directly burned out. What is the reason for this? This small PCB board is wrapped with glue to prevent moisture. Some people analyzed that the glue caused the chip capacitor to deform during the drying process, resulting in damage to the capacitor. Is this possible? Please help me analyze it.

Figure 1 is normal. The capacitor in Figure 2 is burned out.

Figure 1

Figure 2

Adrain_shine

It is possible

迈尔风随

This is possible. You need to look at the curing characteristics of the glue you use to analyze it.

vincentc543

Look at your specifications

Did you use a lower rated voltage and get electrostatically struck?

qwqwqw2088

I think it's a glue problem

Check what glue you used.

Gen_X

Personal opinion:

Judging from the photos, it looks like manual soldering. I think the manual soldering time is too long or the positioning is repeated, which leads to overheating and damage, or it has reached the critical point of failure. After the power is turned on, the damage is aggravated. This kind of capacitor damage usually has a very low resistance, which directly leads to power supply problems. It is relatively rare to self-ignite.

In addition, the failure rate is low and not so high. I do a lot of hand soldering, but I have only seen one case of this capacitor being damaged so far.

se7ens

For safety reasons, two capacitors can be used in series to replace

芯片老兵

Glue damage and heat damage are most likely. You can try it without glue to see if there is any damage and compare it with glue.

chunyang

Mechanical deformation is the main cause of this type of failure, but it is rare for it to be caused by glue. It is necessary to analyze the shrinkage rate of the glue used and the local torque caused.

chunyang

In addition, moisture-proof glue is not suitable. Generally, special three-proof paint or epoxy resin potting is used. These conventional methods will not cause capacitor damage due to mechanical deformation.

吾妻思萌

It doesn't seem to be a glue problem. You can investigate the capacitor batch problem. It may be a DPPM problem of the capacitor quality itself.

With such a large pad, MLCC is relatively mature, and 3V does not consume much power, so it will not cause mechanical deformation due to CTE mismatch.

一叶知秋霜

Ceramic capacitors are easily damaged by mechanical stress, but how can a 3V voltage cause them to burn? This degree of burning is a bit exaggerated. Is there a high voltage coming over?