Explosion of 74HC14 IC in Old Stock

In summary: SMT package has lead frame that is exposed, so leads can oxidize over time. In this particular case, it looks like the leads on the MCU were oxidized which caused intermittent failures.
  • #1
trurle
508
206
TL;DR Summary
Searching mechanism and prevention for observed anomaly with rapid unscheduled disassembly of 74HC14 IC
Recently i am trying to put in use a stock of old 74x series microchips manufactured around ~2000 AD.

Unfortunately, one of microchips 74HC14 (hex schmitt trigger inverter) in SOIC-14 package have exploded in test setup in the moment the power was applied.
Loud "popping" sound, flash of blue light, and corner of package around pin 14 (Vdd), measuring around 2mm, shattered. Exposed lead frame from pins 14 and 13 has no visible damage. Chip appears to be "open circuit" for supply current afterward though.

Did anybody experienced similar behavior before? Any ways to avoid it?

Operating conditions were "normal" - AC-DC voltage converter with 5V output (which turned out to be still ok after incident), and either weak pull-ups or ground ties at schmitt trigger inputs.
 
Engineering news on Phys.org
  • #2
Most likely was inserted in the socket backwards.

2nd most likely, had been previously damaged electrically.

3rd most likely, replace 'backwards', above, with 'incorrectly.'

4th most likely, (the generic answer) manufacturing defect. (This one is especially useful when you don't want to take blame. :wink:)

Cheers,
Tom
 
  • Like
Likes davenn, DaveE and trurle
  • #3
Tom.G said:
Most likely was inserted in the socket backwards.

2nd most likely, had been previously damaged electrically.

3rd most likely, replace 'backwards', above, with 'incorrectly.'

4th most likely, (the generic answer) manufacturing defect. (This one is especially useful when you don't want to take blame. :wink:)

Cheers,
Tom
This is SOIC, not DIP. Connected by reflow soldering without socket.
I checked the orientation and soldering. All pins were connected correctly. This leave electrical (ESD?) damage or manufacturing defect as possible culprits. Never before observed ESD damage to lead to actual explosion though. Usually it results in just non-responsive input.
 
  • #4
Singular event or it happened for more than one IC the similar way?
It may be:
- accident
- since it is from an older stock, maybe popcorn effect? Usually it is just popping, but long term storage might lead to degradation too (=> short circuit => bond wires acts as fuses). Maybe worth checking the other chips from the same stock for cracks.
 
  • #5
Rive said:
Singular event or it happened for more than one IC the similar way?
It may be:
- accident
- since it is from an older stock, maybe popcorn effect? Usually it is just popping, but long term storage might lead to degradation too (=> short circuit => bond wires acts as fuses). Maybe worth checking the other chips from the same stock for cracks.
Singular event in the batch of 5 prototypes.
Regarding popcorn effect - possible indeed. The storage conditions were far from optimal, and duration was too long. Popcorn effect would be more likely at reflow rather than at functional test stage though..
 
  • #6
trurle said:
Summary:: Searching mechanism and prevention for observed anomaly with rapid unscheduled disassembly of 74HC14 IC

AC-DC voltage converter with 5V output (which turned out to be still ok after incident)
What kind of supply? Does it have current-limit capability? Maybe when bringing up old circuits (or even new ones) for the first time, turn the current-limit down and slowly ramp up the voltage to 5V while monitoring the current to look for any issues. That's usually how we first bring up new ASIC prototypes...
 
  • #7
trurle said:
Popcorn effect would be more likely at reflow rather than at functional test stage though..
For the 'pop' part, yes. But it can blow only/if it's powered up. I would check the other ones for cracks and try to find a way to bake the remaining stock before use anyway.
 
  • Like
Likes trurle
  • #8
berkeman said:
What kind of supply? Does it have current-limit capability? Maybe when bringing up old circuits (or even new ones) for the first time, turn the current-limit down and slowly ramp up the voltage to 5V while monitoring the current to look for any issues. That's usually how we first bring up new ASIC prototypes...
Current limiter on 700mA is present, but it is not controllable (hardwired inside power brick). I indeed tested 1st prototype only with workbench power supply at low current limit (20 mA) and it has no issues.
 
  • Like
Likes berkeman
  • #9
Another thing to consider is oxidized leads, we had built a batch of prototypes with 1 year old MCU's that were apparently not sealed properly, everything looked ok till we powered units up and they would randomly roman candle on us. Mind you the MCU didn't blow, it popped the power modules it was driving.

Turned out the problem was oxidized leads on the SMT package combined with a not so aggressive flux meant some of the leads "looked" soldered, but were barely connected and would disconnect with minimal coercion causing many very strange failures till we identified the problem was various MCU leads not connecting properly intermittently.
 
  • Like
Likes trurle
  • #10
essenmein said:
Another thing to consider is oxidized leads, we had built a batch of prototypes with 1 year old MCU's that were apparently not sealed properly, everything looked ok till we powered units up and they would randomly roman candle on us. Mind you the MCU didn't blow, it popped the power modules it was driving.

Turned out the problem was oxidized leads on the SMT package combined with a not so aggressive flux meant some of the leads "looked" soldered, but were barely connected and would disconnect with minimal coercion causing many very strange failures till we identified the problem was various MCU leads not connecting properly intermittently.
Yes, problem with oxidized leads (cold joints) do happen. Usually "roman candle" happens when chips are driven while power rails are disconnected. I think it can be ruled out for my particular case because all inputs of exploded chip were connected through series 1 MOhm resistors.
Anyway, will try to make more prototypes in February after parts will arrive.
 
  • #11
If there are such large impedance's to the I/O then it probably was just a dead chip to begin with, what's that rule, have to fail at the same thing three times to ensure you have a statistically significant result? Another thing to check though is if turning on the supply causes an initial overshoot or something that may have cooked it.
 
  • Like
Likes trurle
  • #12
essenmein said:
If there are such large impedance's to the I/O then it probably was just a dead chip to begin with, what's that rule, have to fail at the same thing three times to ensure you have a statistically significant result? Another thing to check though is if turning on the supply causes an initial overshoot or something that may have cooked it.
The second prototype batch of 3 (including reworked power supply brick of module which contained exploded chip) have survived qualification. Therefore, the preliminary decision is "a singular accident due dead chip".
 
  • Like
  • Informative
Likes Asymptotic and berkeman

1. Why did the 74HC14 IC explode in old stock?

The most likely reason for an explosion in an old 74HC14 IC is due to the buildup of moisture or other contaminants inside the IC. This can cause a short circuit and lead to an explosion.

2. Can the 74HC14 IC be salvaged after an explosion?

In most cases, an exploded 74HC14 IC cannot be salvaged and will need to be replaced. The explosion can cause damage to the internal components and render the IC unusable.

3. How can I prevent explosions in old stock 74HC14 ICs?

To prevent explosions in old stock 74HC14 ICs, it is important to store them in a dry and clean environment. Avoid exposing them to moisture or other contaminants, and regularly check the expiration date on the ICs.

4. Is it safe to use old stock 74HC14 ICs?

It is generally not recommended to use old stock 74HC14 ICs, especially if they have been stored for a long time or have visible signs of damage. It is best to replace them with new ICs to ensure safety and proper functioning.

5. Can other factors, besides moisture, cause an explosion in old stock 74HC14 ICs?

Yes, other factors such as excessive heat or voltage spikes can also cause an explosion in old stock 74HC14 ICs. It is important to handle and store these ICs carefully to avoid any potential damage.

Hot Threads

Recent Insights

Back
Top