Unofficial FAQ: Ignition corrections
#46
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Posts: n/a
Re: Unofficial FAQ: Ignition corrections
jim beam <nospam@example.net> wrote in
news:a-CdnfV0hNx07C7fRVn-iQ@speakeasy.net:
> Michael Pardee wrote:
>> <r2000swler@hotmail.com> wrote in message
>> news:1118859696.926058.152280@z14g2000cwz.googlegr oups.com...
>>
>>>One important point is that it looks like Honda skimps on teh heat
>>>sink compound. Of course the engine runs hotter then the igniter, so
>>>I am not at all sure that adding more thermal coupling will help. I
>>>have thought
>>>of adding a "heat pipe" tp remove heat from the igniter. I now
>>>consider the
>>>igniter a subsystem that is doomed to failure. It simply operates too
>>>hot
>>>for prolonged life.
>>>
>>
>>
>> I don't think the heat is too great for the ignitor. There apparently
>> aren't any electrolytic capacitors in it, and those are the big heat
>> sensitive worries.
>>
>> The vulnerability of transistors to heat is related to junction
>> temperature and to collector voltage. When the collector junction
>> gets hot enough, the reverse voltage across it can make the dopants
>> migrate and "blur" the junction. That spot gets hotter and eventually
>> melts, leading to the device being shorted.
>
> the "blurring" is diffusion - the operating temp doesn't even get
> close to melting - but diffusion is powerful stuff and it definitely
> destroys semiconductors.
>
>>
>> But the heat required to melt the junction without the voltage stress
>> is much higher than your engine compartment - the melting point of
>> silicon is over 2500 degrees F. The silicon chips are typically
>> soldered to the heat sink internally, and I have personally soldered
>> a UHF power transistor to a large copper heatsink with an acetylene
>> torch.
>
> the two factors at play are temperature & time. if the device was
> physically big enough and you solderd quick enough, there's no reason
> you couldn't do it - afterall, what temperature does a silcon foundry
> work at? but you got to be /quick/ if you go to high temps. or best
> not at all if you want good service life.
>
>>
>> Mike
>>
>>
>
>
Even the best heat sink does not conduct all the heat away from a
semiconductor junction.The semi junction temp increase is probably faster
than what the HS can conduct away,and having a higher base temp would make
that occur faster.
--
Jim Yanik
jyanik
at
kua.net
news:a-CdnfV0hNx07C7fRVn-iQ@speakeasy.net:
> Michael Pardee wrote:
>> <r2000swler@hotmail.com> wrote in message
>> news:1118859696.926058.152280@z14g2000cwz.googlegr oups.com...
>>
>>>One important point is that it looks like Honda skimps on teh heat
>>>sink compound. Of course the engine runs hotter then the igniter, so
>>>I am not at all sure that adding more thermal coupling will help. I
>>>have thought
>>>of adding a "heat pipe" tp remove heat from the igniter. I now
>>>consider the
>>>igniter a subsystem that is doomed to failure. It simply operates too
>>>hot
>>>for prolonged life.
>>>
>>
>>
>> I don't think the heat is too great for the ignitor. There apparently
>> aren't any electrolytic capacitors in it, and those are the big heat
>> sensitive worries.
>>
>> The vulnerability of transistors to heat is related to junction
>> temperature and to collector voltage. When the collector junction
>> gets hot enough, the reverse voltage across it can make the dopants
>> migrate and "blur" the junction. That spot gets hotter and eventually
>> melts, leading to the device being shorted.
>
> the "blurring" is diffusion - the operating temp doesn't even get
> close to melting - but diffusion is powerful stuff and it definitely
> destroys semiconductors.
>
>>
>> But the heat required to melt the junction without the voltage stress
>> is much higher than your engine compartment - the melting point of
>> silicon is over 2500 degrees F. The silicon chips are typically
>> soldered to the heat sink internally, and I have personally soldered
>> a UHF power transistor to a large copper heatsink with an acetylene
>> torch.
>
> the two factors at play are temperature & time. if the device was
> physically big enough and you solderd quick enough, there's no reason
> you couldn't do it - afterall, what temperature does a silcon foundry
> work at? but you got to be /quick/ if you go to high temps. or best
> not at all if you want good service life.
>
>>
>> Mike
>>
>>
>
>
Even the best heat sink does not conduct all the heat away from a
semiconductor junction.The semi junction temp increase is probably faster
than what the HS can conduct away,and having a higher base temp would make
that occur faster.
--
Jim Yanik
jyanik
at
kua.net
#47
Guest
Posts: n/a
Re: Unofficial FAQ: Ignition corrections
jim beam <nospam@example.net> wrote in
news:a-CdnfV0hNx07C7fRVn-iQ@speakeasy.net:
> Michael Pardee wrote:
>> <r2000swler@hotmail.com> wrote in message
>> news:1118859696.926058.152280@z14g2000cwz.googlegr oups.com...
>>
>>>One important point is that it looks like Honda skimps on teh heat
>>>sink compound. Of course the engine runs hotter then the igniter, so
>>>I am not at all sure that adding more thermal coupling will help. I
>>>have thought
>>>of adding a "heat pipe" tp remove heat from the igniter. I now
>>>consider the
>>>igniter a subsystem that is doomed to failure. It simply operates too
>>>hot
>>>for prolonged life.
>>>
>>
>>
>> I don't think the heat is too great for the ignitor. There apparently
>> aren't any electrolytic capacitors in it, and those are the big heat
>> sensitive worries.
>>
>> The vulnerability of transistors to heat is related to junction
>> temperature and to collector voltage. When the collector junction
>> gets hot enough, the reverse voltage across it can make the dopants
>> migrate and "blur" the junction. That spot gets hotter and eventually
>> melts, leading to the device being shorted.
>
> the "blurring" is diffusion - the operating temp doesn't even get
> close to melting - but diffusion is powerful stuff and it definitely
> destroys semiconductors.
>
>>
>> But the heat required to melt the junction without the voltage stress
>> is much higher than your engine compartment - the melting point of
>> silicon is over 2500 degrees F. The silicon chips are typically
>> soldered to the heat sink internally, and I have personally soldered
>> a UHF power transistor to a large copper heatsink with an acetylene
>> torch.
>
> the two factors at play are temperature & time. if the device was
> physically big enough and you solderd quick enough, there's no reason
> you couldn't do it - afterall, what temperature does a silcon foundry
> work at? but you got to be /quick/ if you go to high temps. or best
> not at all if you want good service life.
>
>>
>> Mike
>>
>>
>
>
Even the best heat sink does not conduct all the heat away from a
semiconductor junction.The semi junction temp increase is probably faster
than what the HS can conduct away,and having a higher base temp would make
that occur faster.
--
Jim Yanik
jyanik
at
kua.net
news:a-CdnfV0hNx07C7fRVn-iQ@speakeasy.net:
> Michael Pardee wrote:
>> <r2000swler@hotmail.com> wrote in message
>> news:1118859696.926058.152280@z14g2000cwz.googlegr oups.com...
>>
>>>One important point is that it looks like Honda skimps on teh heat
>>>sink compound. Of course the engine runs hotter then the igniter, so
>>>I am not at all sure that adding more thermal coupling will help. I
>>>have thought
>>>of adding a "heat pipe" tp remove heat from the igniter. I now
>>>consider the
>>>igniter a subsystem that is doomed to failure. It simply operates too
>>>hot
>>>for prolonged life.
>>>
>>
>>
>> I don't think the heat is too great for the ignitor. There apparently
>> aren't any electrolytic capacitors in it, and those are the big heat
>> sensitive worries.
>>
>> The vulnerability of transistors to heat is related to junction
>> temperature and to collector voltage. When the collector junction
>> gets hot enough, the reverse voltage across it can make the dopants
>> migrate and "blur" the junction. That spot gets hotter and eventually
>> melts, leading to the device being shorted.
>
> the "blurring" is diffusion - the operating temp doesn't even get
> close to melting - but diffusion is powerful stuff and it definitely
> destroys semiconductors.
>
>>
>> But the heat required to melt the junction without the voltage stress
>> is much higher than your engine compartment - the melting point of
>> silicon is over 2500 degrees F. The silicon chips are typically
>> soldered to the heat sink internally, and I have personally soldered
>> a UHF power transistor to a large copper heatsink with an acetylene
>> torch.
>
> the two factors at play are temperature & time. if the device was
> physically big enough and you solderd quick enough, there's no reason
> you couldn't do it - afterall, what temperature does a silcon foundry
> work at? but you got to be /quick/ if you go to high temps. or best
> not at all if you want good service life.
>
>>
>> Mike
>>
>>
>
>
Even the best heat sink does not conduct all the heat away from a
semiconductor junction.The semi junction temp increase is probably faster
than what the HS can conduct away,and having a higher base temp would make
that occur faster.
--
Jim Yanik
jyanik
at
kua.net
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