Groups > sci.electronics.components > #5955

Re: Replacement LED?

From	Jeff Liebermann <jeffl@cruzio.com>
Newsgroups	sci.electronics.components, sci.electronics.design, sci.electronics.repair, alt.engineering.electrical
Subject	Re: Replacement LED?
Date	2016-03-31 08:34 -0700
Message-ID	<2cfqfbhsmpru7a3ei55dp4e5a5scduhddq@4ax.com> (permalink)
References	<0001HW.1CA0671B00048EC510F3873CF@news.eternal-september.org> <5ne1fbt0u9qop3jmdkdd18go76did4csr3@4ax.com> <slrnnfdqas.8nq.cheney@atc5.vermine.org> <02ojfb9j4dpfc04mr0fdc93nqhio94g076@4ax.com> <KpidnWOVipVoQGHLnZ2dnUU7-fudnZ2d@earthlink.com>

Cross-posted to 4 groups.

Show all headers | View raw

On Thu, 31 Mar 2016 04:20:59 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

>
>Jeff Liebermann wrote:
>> 
>> On Sat, 26 Mar 2016 19:56:12 +0000 (UTC), Andre Majorel
>> <cheney@halliburton.com> wrote:
>> 
>> Sorry for the delay but I missed the followups to my comment.
>> 
>> >On 2016-03-22, Jeff Liebermann <jeffl@cruzio.com> wrote:
>> >
>> >> If it uses an MLCC capacitor, use a hot air gun to reflow, not
>> >> a soldering iron tip.
>> >
>> >News to me. In what way are multi-layer ceramic caps and
>> >soldering irons incompatible ?
>> 
>> Thermal shock easily cracks MLCC caps.  I learned that the hard way
>> while fixing several Apple Mac Mini computahs, which feature a
>> collection of MLCC on the bottom of the main board.
>> <https://web.archive.org/web/20130606062903/http://blog.helpmymac.ru/?p=3585>
>> The original failure mode was shorted MLCC caps caused by either
>> thermal shock or board flex.  The bad ones were easy to find with an
>> ESR meter.  However, when I tried to install replacements (and
>> guessing the part value because Apple doesn't supply service
>> information to non-authorized repair shops), I managed to crack and
>> short several known good MLCC caps with a soldering iron.  Having
>> learned the lesson, I used some solder paste and a hot air SMT reflow
>> gun to do the soldering.  I also pre-heated the PCB and let the caps
>> cool down slowly.  I don't know if that was necessary, but it worked
>> every time.  I'm told that two solding irons used as a tweezer also
>> works, but I haven't tried that yet.

>How were the new caps stored? If it is where they can adsorb
>moisture, you can damage them with an iron that is too hot.

Well, I must admit that I didn't take any special precautions.
Methinks that the relative humidity in my office runs between 40% and
60% but is not monitored or recorded.  Occasionally, it gets low
enough to where static electricity becomes a problem, or high enough
to where I'm rather uncomfortable, but those are rare.  The caps a mix
of cut tape and loose bags stored in Ziploc bags (mostly pink
anti-static) and in paper coin envelopes.  Nothing in hard plastic or
metal drawers that might chip or crack them.  Although I know that
these caps make tolerable hydrometers (and microphones), I don't think
they can absorb enough moisture from the air to where a steam
explosion would be a problem.  

I did some digging to see if humidity might be a problem in storage
conditions.  There were plenty of notes on how a cracked capacitor
might allow water to enter the dielectric.  Soft (solder) termination
is the recommended fix.  Some suggests pre-heating the capacitors
before soldering to drive off any moisture.  One demands that the caps
be used within 12 months.  I didn't see humidity as being a problem
until AFTER the capacitors had cracked.  It would take some time for
the moisture to alter the capacitor characteristics.  With my hand
soldering technique, I managed to instantly produce shorted
capacitors, which methinks was more likely due to uneven thermal
expansion, than to moisture incursion.

-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Thread

Replacement LED? DaveC <not@home.cow> - 2016-03-21 10:30 -0700
  Re: Replacement LED? Bob Engelhardt <BobEngelhardt@comcast.net> - 2016-03-21 17:00 -0400
  Re: Replacement LED? John Larkin <jjlarkin@highlandtechnology.com> - 2016-03-21 20:05 -0700
  Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-21 20:51 -0700
    Re: Replacement LED? DaveC <not@home.cow> - 2016-03-21 22:56 -0700
      Re: Replacement LED? N_Cook <diverse@tcp.co.uk> - 2016-03-22 15:42 +0000
      Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-22 16:42 -0700
        Re: Replacement LED? DaveC <not@home.cow> - 2016-03-22 16:56 -0700
          Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-22 18:16 -0700
            Re: Replacement LED? DaveC <not@home.cow> - 2016-03-22 18:56 -0700
              Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-23 11:11 -0700
                Re: Replacement LED? DaveC <not@home.cow> - 2016-03-23 21:50 -0700
                Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-23 22:49 -0700
                Re: Replacement LED? DaveC <not@home.cow> - 2016-03-24 14:02 -0700
        Re: Replacement LED? not@telling.you.invalid (Computer Nerd Kev) - 2016-03-24 21:44 +0000
    Re: Replacement LED? Syd Rumpo <usenet@nononono.co.uk> - 2016-03-22 09:10 +0000
      Re: Replacement LED? DaveC <not@home.cow> - 2016-03-22 13:41 -0700
        Re: Replacement LED? rickman <gnuarm@gmail.com> - 2016-03-22 21:46 -0400
          Re: Replacement LED? DaveC <not@home.cow> - 2016-03-22 19:00 -0700
            Re: Replacement LED? rickman <gnuarm@gmail.com> - 2016-03-23 00:19 -0400
              Re: Replacement LED? DaveC <not@home.cow> - 2016-03-22 22:23 -0700
                Re: Replacement LED? DaveC <not@home.cow> - 2016-03-23 11:52 -0700
              Re: Replacement LED? "Ralph Mowery" <rmowery28146@earthlink.net> - 2016-03-23 10:31 -0400
    Re: Replacement LED? Andre Majorel <cheney@halliburton.com> - 2016-03-26 19:56 +0000
      Re: Replacement LED? John Larkin <jjlarkin@highlandtechnology.com> - 2016-03-27 10:20 -0700
      Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-28 19:21 -0700
        Re: Replacement LED? "Michael A. Terrell" <mike.terrell@earthlink.net> - 2016-03-31 04:20 -0400
          Re: Replacement LED? Jeff Liebermann <jeffl@cruzio.com> - 2016-03-31 08:34 -0700
          Re: Replacement LED? krw <krw@nowhere.com> - 2016-03-31 20:10 -0400
            Re: Replacement LED? "Michael A. Terrell" <mike.terrell@earthlink.net> - 2016-04-01 17:21 -0400
              Re: Replacement LED? krw <krw@nowhere.com> - 2016-04-01 19:14 -0400
                Re: Replacement LED? "Michael A. Terrell" <mike.terrell@earthlink.net> - 2016-04-01 19:43 -0400
        Re: Replacement LED? Andre Majorel <cheney@halliburton.com> - 2016-03-31 10:40 +0000

csiph-web