How are diodes and thermistors encased in glass?

I have an application where I have to replace a temperature sensor with a
glass one to provide better immunity to liquids:

MF58 NTC Thermistors High Sensitivity 1% Accuracy
https://www.amazon.ca/gp/product/B07Z3DPJNX/

Looking at the sensor, it occurs to me that the temperature needed to bond
the glass to the leads would destroy the sensor.

I searched for low temperature glass to find the temperature, but the lowest
temperature I could find was around 400C:

https://www.ep.neg.co.jp/en-powder-glass01

Wouldn't that temperature destroy the sensor?

Thanks,

Mike

--
MRM

Mike Monett VE3BTI wrote:
===========================
> How are diodes and thermistors encased in glass?
>

** Done in several steps, such that molten glass never contacts delicate parts.
> I have an application where I have to replace a temperature sensor with a
> glass one to provide better immunity to liquids:

** Glass bead thermistors look just like tiny light bulbs.

.....Phil

On Tuesday, September 27, 2022 at 10:50:48 PM UTC, Mike Monett VE3BTI wrote:
> How are diodes and thermistors encased in glass?
> I have an application where I have to replace a temperature sensor with a
> glass one to provide better immunity to liquids:
> MF58 NTC Thermistors High Sensitivity 1% Accuracy
> https://www.amazon.ca/gp/product/B07Z3DPJNX/
> Looking at the sensor, it occurs to me that the temperature needed to bond
> the glass to the leads would destroy the sensor.
> I searched for low temperature glass to find the temperature, but the lowest
> temperature I could find was around 400C:
> https://www.ep.neg.co.jp/en-powder-glass01
> Wouldn't that temperature destroy the sensor?
> Thanks,
> Mike
> MRM

If we zoom in a bit we can see the copper slugs
on each side of the chip, and each lead exiting
axially from a slug. Idea is..
The slugs are heat sinks
and keep the temperature at the chip
to within a safe level while the glass ends
are sealed (quickly).

On Wednesday, 28 September 2022 at 00:55:33 UTC+1, Rich S wrote:
> On Tuesday, September 27, 2022 at 10:50:48 PM UTC, Mike Monett VE3BTI wrote:
> > How are diodes and thermistors encased in glass?
> > I have an application where I have to replace a temperature sensor with a
> > glass one to provide better immunity to liquids:
> > MF58 NTC Thermistors High Sensitivity 1% Accuracy
> > https://www.amazon.ca/gp/product/B07Z3DPJNX/
> > Looking at the sensor, it occurs to me that the temperature needed to bond
> > the glass to the leads would destroy the sensor.
> > I searched for low temperature glass to find the temperature, but the lowest
> > temperature I could find was around 400C:
> > https://www.ep.neg.co.jp/en-powder-glass01
> > Wouldn't that temperature destroy the sensor?
> > Thanks,
> > Mike
> > MRM
>
> If we zoom in a bit we can see the copper slugs
> on each side of the chip, and each lead exiting
> axially from a slug. Idea is..
> The slugs are heat sinks
> and keep the temperature at the chip
> to within a safe level while the glass ends
> are sealed (quickly).

The leads are likely to be made from covar plated with copper and
maybe tin. This is an iron-based alloy, so it can corrode if it is allowed
to remain wet for a long time. Also, the resistance will be altered if
there is a continuous film of water on the glass.

John

Mike Monett VE3BTI <spamme@not.com> wrote:

> Looking at the sensor, it occurs to me that the temperature needed to
> bond the glass to the leads would destroy the sensor.
>
> I searched for low temperature glass to find the temperature, but the
> lowest temperature I could find was around 400C:
>
> https://www.ep.neg.co.jp/en-powder-glass01
>
> Wouldn't that temperature destroy the sensor?

Found the answer for diodes:

Quote:

The silicon wafer or bead can withstand 900�C but the critical process is
the low temp interlayer powdered glass that is now Pb-free using Bismuth
and other metals mixed with Silicon Dioxide. This passivation layer reduces
the high temp leakage and limits most diodes to 200�C or less. The outer
layer of glass is then molded with powdered SiO2 to form the shape that
appears. The trade secrets are in the passivation blends of powder ,
cleaning processes and standard wire bonding to the melted gold bond to the
crystal.

https://electronics.stackexchange.com/questions/381132/how-are-glass-
diodes-produced

I can't find any information on thermistors, but I have to assume they are
much simpler than semiconductors, and should easily survive the glass
bonding temperature.

--
MRM

On 2022-09-28, Mike Monett VE3BTI <spamme@not.com> wrote:
> Mike Monett VE3BTI <spamme@not.com> wrote:
>
>> Looking at the sensor, it occurs to me that the temperature needed to
>> bond the glass to the leads would destroy the sensor.
>>
>> I searched for low temperature glass to find the temperature, but the
>> lowest temperature I could find was around 400C:
>>
>> https://www.ep.neg.co.jp/en-powder-glass01
>>
>> Wouldn't that temperature destroy the sensor?
>
> Found the answer for diodes:
>
> Quote:
>
> The silicon wafer or bead can withstand 900’C but the critical process is
> the low temp interlayer powdered glass that is now Pb-free using Bismuth
> and other metals mixed with Silicon Dioxide. This passivation layer reduces
> the high temp leakage and limits most diodes to 200’C or less. The outer
> layer of glass is then molded with powdered SiO2 to form the shape that
> appears. The trade secrets are in the passivation blends of powder ,
> cleaning processes and standard wire bonding to the melted gold bond to the
> crystal.
>
> https://electronics.stackexchange.com/questions/381132/how-are-glass-
> diodes-produced
>
> I can't find any information on thermistors, but I have to assume they are
> much simpler than semiconductors, and should easily survive the glass
> bonding temperature.

You'd be right. platinum can witstand higher temperatures than iron
(before melting), higher than silica even. (just)

--
Jasen.

Jasen Betts <usenet@revmaps.no-ip.org> wrote:

>> I can't find any information on thermistors, but I have to assume they
>> are much simpler than semiconductors, and should easily survive the
>> glass bonding temperature.
>
> You'd be right. platinum can witstand higher temperatures than iron
> (before melting), higher than silica even. (just)

I don't understand why, but asking the same question again gave vastly
different results. There is a huge amount of information available on
thermistors. They are basically metal oxides sintered into the desired
shape and covered with a protective coating. Being oxides, the can easily
withstand the high temperature of glass bonding. Problem solved.

Thanks for your reply.

Here are some examples:

1. Materials typically involved in the fabrication of NTC resistors are
platinum, nickel, cobalt, iron and oxides

https://eepower.com/resistor-guide/resistor-types/ntc-thermistor/#

2. The sensing element is basically a thermal resistor made with sintering
(pressing) mixtures of metallic oxides like copper, nickel, cobalt, iron,
manganese, and uranium.

https://www.electricaldeck.com/2021/06/thermistor-construction-types-
working-characteristics-applications.html

3. Negative Temperature Coefficient or NTC Thermistor :

NTC thermistors are made of oxides of Mn, Ni, Co, Uranium which are milled
in proper proportions with binders, pressed into the desired shape, and
sintered.

Positive Temperature Coefficient or PTC Thermistor :

These are usually made from titanates of barium, lead, and strontium.

https://www.electricaldeck.com/2021/06/thermistor-construction-types-
working-characteristics-applications.html

--
MRM