Diode LL4148 SOD-80 (mini-melf) goes out of order (craks or breaks down)

Hello.
We have a problem with the diode LL4148 (Vishay or Diotec, we use diodes from both manufacturers).

Sometimes diodes goes out of order in different unrelated PCBs. These PCBs have different topology and schematics. Therefore, the problem is unlikely related with voltage or current surges. Sometimes diodes split (break physically) after soldering, sometimes they go out of order (electrical breakdown) after few hours/days/monthes of work. Seems, that there is a little correlation with manual soldering (we still use it for small parties of PCBs).
Have anyone ever faced with a problem of diodes reliability in sod-80 (mini-melf) or particular with LL4148? Is glass sod-80 less robust then other types of cases? I'm thinking about changing LL4148 on another more reliable and robust case.

Hi,

it sounds like a mechanical problem. Maybe related to hand soldering.

I never had those problems, mot with reflow, not with hand soldering.

But there are 4148 compatible diodes in various packages.
* TS4148R in 1206 (should fit on SOD-80 pads)
* 1N4148WS in SOT323 (Smaller than SOD-80, try if it fits)
* 1N4148W-7 in SOD123 (should fit on SOD-80 pads)
... and others.

They may have their benifits in hand soldering.

Klaus

If you can you could try soldering only one side of the diode and wait for it to cool down for a while and then see if there is a gap between the other side of the diode and the pad. The gap might be very small so you may need something thin to try to slide under it when it's still hot and then again when it's cooled down ( if you can't see a gap by eye). The solder could be shrinking and trying to bend the diode. If there is high vibration they can also break.

Since the SOD80 is glass package, it is sensitive to mechanical stress, specifically board flexing.

We had a similar problem with these same diodes. The long term solution was to replace them with a SOD123 plastic package.

The board footprint has to be adjusted slightly.

I don't think anybody has a happy story about glass
packages. They are universally abhorred in high reliability
applications. Have had package vendors who swore up
and down that their glass-seal package was qualifiable,
fail and fail and fail until we had to pony up money for
a ceramic design. The consistent use of future tense
should have been warning enough.

apprenticemart2 said:

If you can you could try...

Click to expand...

apprenticemart2 said:

If you can you could try...

Click to expand...

Thank you for interesting idea. However, I believe, that gap will depend only on a type of solder and wetting area on a diode pad and a PCB pad. The suggested experiment will not prove that the glass SOD-80 is less robust than an another case.

We have used these on various pcb designs with no more failures than with other diode package types. Ours are machine placed and soldered in reflow oven - usually in pcb batches of 1000 assemblies at a time with several of these parts per assembly. They are NOT palced enar the edge of a PCB, or on long PCBs that are not supported or could be subject to much flexing.

Vasilevski said:

Thank you for interesting idea. However, I believe, that gap will depend only on a type of solder and wetting area on a diode pad and a PCB pad. The suggested experiment will not prove that the glass SOD-80 is less robust than an another case.

Click to expand...

I was suggesting that you may be able to detect solder shrinkage by only soldering one side of the part and leaving it to cool.
Because these packages are for wave soldering or more likely these days for paste, when you hand solder them you will be applying solder higher up the part and this could mean that the shape of the solder 'weld' is different to how it would be if paste was used. Also you are not heating up the whole diode and pcb as it would be done in an oven, in a controlled manner with set heating/cooling curves. As others have mentioned, it seems you need to use a different package.

apprenticemart2 said:

Because these packages are for wave soldering or more likely these days for paste

Click to expand...

Where you have found such information? I have examined the LL4148-GS08 datasheet carefully and I haven't found any mention about type of soldering.