Longevity of SMDs

[lars-musik]

Summary: A SMD 1206 capacitor went belly up for no good reason.

Long story: I spent 4 hours debugging a 1590a built of the Clarin(not)³ last night without success. Everything worked fine, then I put the board into the enclosure and the sound was crackly. So everything out of the box again and a visual check on the wiring. I tried to keep the cables to the pots as short as possible and that put quite some tension on the wiring so I thought one could have come loose. I re-wired one pot after another - still no success. The sound became very faint and quite distorted by then. Then I replaced the main chip. Then I searched for my audioprobed - also unsuccessful on my chaotic workbench. OK. I soldered a new audioprobe  an FINALLY found that the sound stopped after C4. I re-soldered the joints. No good. In the end, the capacitor just was kaput. How is that possible? I finished the build a week ago and tried it from time to time. It worked since days. I applied no heat and no pressure on that part during the housing process. I am baffled.

Question: How is that possible and how to avoid it?

[Groovenut]

I'm going to assume the cap was a MLCC, is it possible that it was overheated during soldering? Or was cracked somehow during install? Or maybe from the factory that way?

[J0K3RX]

I'm going to assume the cap was a MLCC, is it possible that it was overheated during soldering? Or was cracked somehow during install? Or maybe from the factory that way?

Agree with Lawrence. I have seen many SMD parts with hair line fractures in them usually you can't see the fracture until you remove them and the component comes off in 2 pieces. Usually the little SMD caps can take a lot of heat but never know...

[deadastronaut]

^ tell me about it...just got 2 arduino nano clones from china...

had my first experience with smd...not by choice

sorted now though...

[lars-musik]

It indeed fell apart during removal.

A cap came off the cap. Crap.

[amptramp]

SMD devices are often at the hairy edge of what they can tolerate during soldering, especially when using lead-free solder which melts at a higher temperature.  Also, any flexure of the board and stuff tends to come apart.  Components with leads do not tend to have these problems.

[R.G.]

Components with leads do not tend to have these problems.

This is because the length of lead allows much more flex before exceeding the strength of the solder joint or metallization end caps on the parts. The leads add what's called "compliance" in the ME biz.

[amptramp]

Components with leads do not tend to have these problems.

This is because the length of lead allows much more flex before exceeding the strength of the solder joint or metallization end caps on the parts. The leads add what's called "compliance" in the ME biz.

One of the requirements in certain military standards is that a strain relief should be incorporated in component assembly.  This was usually as simple as bending a component lead.  Even some cordwood assemblies had a "U" shape bent into each lead.  Some surface-mount flatpacks have gullwing leads coming out of the side that allows some flexure but no passive component has this.  Hybrid circuits have a ceramic substrate that tends to track the movement of ceramic components but not epoxy components.

[lars-musik]

  Also, any flexure of the board and stuff tends to come apart.

That might have been the reason. I changed from 1.5 mm epoxy boards to 0.8 mm (less dust during sawing and drilling, less wear on the drills, less space in the enclosure) and they bend quite easily. Next order will be 1.5mm boards again.

[TooManyKnobs]

Smaller SMT passives are less prone to crack due to board flex as well but that brings on a new set of annoying issues.