[time-nuts] Wenzel Oscillator Repair

[Chuck Harris]

Hi Joe,

When you preheat to 105C, you don't need to travel as far to
reach the melting point of the solder as you do from room
temperature (25C).  That makes a big difference in how much
power you need to couple into the joint to make it melt.

If you go straight to the torch, and use the brute force
supply of energy to make the joint melt quickly, you will
overshoot the temperature every time.  A couple of seconds
too long, and you can make quite a mess.

I've done it both ways, with the torch, you are moving very
quickly, and making hasty yanks and grabs to try and remove the
cover as quickly as possible.  With preheat you can move
leisurely, and use a small iron, or hot air gun, to provide
the additional calories needed to melt the solder.

Preheat is best by a long shot.  Try it and I am sure you
will agree.

-Chuck Harris

Joseph M Gwinn wrote:
> Chuck,
> 
> 
> time-nuts-bounces at febo.com wrote on 01/21/2009 11:34:41 AM:
> 
>> Hi Joe,
>>
>> Nope, Magnus is talking about foam insulated hermetically sealed
>> ocxo's.
>>
>> The point you are missing is the preheater is only set for a temperature
>> that the foam, etc. can take on a continuous basis... such as +105C.
>> This preheat reduces the amount of additional heat that must be added
>> to make the solder melt.  The net result is usually so nice that you
>> cannot even tell the foam has even been heated.
> 
> That the foam must handle the oven temperature is a good point.  Certainly 
> some preheat can help, but typical 63-37 eutectic solder melts at 183 C, 
> and for reasonable speed one must heat the metal at least 50 C hotter, and 
> soldering irons are run at 310 C (590 F, 600 F being typical).  The solder 
> used on the cans I've seen looks more like 60-40 radio solder, so higher 
> temperatures may be needed.  It's less damaging to go a bit high than a 
> bit low, because if one is high, the can cover still comes off quickly. 
> And the faster this is done, the better.
> 
> One preheats circuit boards to about 115C before soldering, if only to 
> ensure that all moisture is driven off.  So 105C is in the range.
> 
> Joe
> 
> 
> 
>> -Chuck Harris
>>> I think we are talking about different things.  For getting chips off 
> a 
>>> big multilayer board, preheat plus hot air is a standard way to go, 
> but we 
>>> are talking about how to unsolder a steel can with foam insulation 
> within. 
>>>  Slow heating to near soldering temperature is likely to yield a heap 
> of 
>>> goo. 
>>>
>>> The point of the torch method is to heat the can's solder seam up 
> *fast*, 
>>> so the solder melts before the foam.
>>>
>>> Joe
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-
>> bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-
>> bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>