On Thu, 28 Apr 2022 20:03:56 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Tuesday, April 26, 2022 at 2:13:58 PM UTC-7, John Larkin wrote:
>> On Tue, 26 Apr 2022 20:50:58 -0000 (UTC),
>> DecadentLinux...@decadence.org wrote:
>
>> Do you design with melfs? Why?
>> >
>> > They were to replicate the design and features of glass encapsulated,
>> >hermetically sealed components like diodes and such.
>
>> Why?
>
>The glass package is thermally better than epoxies (or used to be)
>and extremely well sealed against contaminants. Classic diode test: run
>ten or twenty amps through a 1N4007 until you hear a 'pow' and see smoke.
>Then put it on a curve tracer. It still works normally (underneath the epoxy,
>the package was plug-sealed glass). The epoxy is burnt and cracked, though.

Do design with melfs?

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

On Fri, 29 Apr 2022 17:28:25 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

>On 29/04/2022 15:38, jlarkin@highlandsniptechnology.com wrote:
>> On Fri, 29 Apr 2022 10:17:17 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> Clive Arthur wrote:
>>>> On 25/04/2022 14:58, jlarkin@highlandsniptechnology.com wrote:
>>>>> On Fri, 22 Apr 2022 08:02:05 -0700 (PDT), "neo5...@gmail.com"
>>>>> <neo5bass@gmail.com> wrote:
>>>>>
>>>>>> I suspect if a real source is around, no one wants to tell, but I am
>>>>>> having a hard time trying to get simple passive components. Melf
>>>>>> resistors, Pulse resistant resistors stuff like that.
>>>>>> Are there any places selling basic components besides E-Bay?
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>> Don
>>>>>
>>>>> Why melfs?
>>>>>
>>>>> The x-chapters (H+H) have some great data on resistor overload.
>>>>
>>>> MELFs dissipate more for a given footprint and can take a bigger solder
>>>> fillet which holds them in place better under high vibration,
>>>> particularly when the solder's weakened at high temperatures, and if
>>>> potted, there's more body for the potting to hold.
>>>>
>>>> They're also much prettier.
>>>>
>>>> Personally, I find them easier to handle if I have to replace one
>>>> because there's more to grip, but that's a trivial concern.
>>>>
>>>> But they have been noticeably harder to obtain for a few years.
>>>>
>>>> Q. Were MELFs originally made that way because they're essentially
>>>> leaded parts without the leads?  [It goes full circle - chop open a
>>>> leaded dipped ceramic capacitor and you'll often find inside a surface
>>>> mount part with leads soldered/welded on.]
>>>
>>> Yup. At one point some bright outfit was selling MELFs with square end
>>> caps to prevent them from rolling around. Dunno if they're still available.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> There are some diodes like that, thin end plates.
>>
>> Hard potting compounds sometimes expand as they cure, and cure
>> non-uniformly. Imagine potting getting under such a melf and
>> fracturing the skinny pin plating.
>>
>> https://www.apogeeweb.net/ModelImgs/BigIMG/J/JAN1N5811US.jpg
>>
>> Potting is bad news in general.
>
>It's horrible, but necessary in high shock/vibration equipment. We use
>RTV, as far as I know everyone does for high temperature high shock.
>
>[Actually, it's easier to clean a MELF populated board properly too,
>though that's a very marginal advantage as there will always be lots of
>'ordinary' SM parts too.]

Melfs might be better for high voltage or pA circuits, because they
probably clean better.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon