soldering iron & advice for magnifier

From: J.C. Wren <jcwren_at_jcwren.com>
Date: Sat May 15 13:43:48 2004

Brad Parker wrote:

>Tom Uban wrote:
>
>
>>>I'm not familiar with Metcal units. How would the MX1 compare with the
>>>Weller WES51 I recently bought?
>>>
>>>
>>I don't know much about the WES51, but the Metcal is an RF driven device
>>and it heats up immediately and maintains the temperature of the specific
>>
>>
>
>The WES51 is "ok" (I have one), but it's not extremely accurate temp
>wise and the smallest tips are small, but not extremely sharp. I'd call
>it the Volkswagon. Dependable, cheap, works well.
>
>The Metcal is the Porsche. Nice design, nice egonometrics, very fast,
>very reliable, really, really nice.
>
>just my opinion, but I've used both.
>
>(and I'm still kicking myself for not buying a couple of used metcal's for
>pennies on the dollar a few years ago - what was thinking?!)
>
>-brad
>
>
>
    I've had a Metcal MX-500 for several years, and along with a RM3E
wand, a set of Talons. The Talons are "hot tweezers" and are invaluable
for removing Rs, Cs, and SOICs. Along with this I have a Nikon SMZ-2B
microscope with a remote light source, a Taiwanese knock-off of the
Hakko 852 hot air machine (the Hakko is definitely better), and a EFD
1500 XL paste dispenser (all from eBay!). With this combination, you can
do just about everything except BGA. I'm not the least bit afraid of
SMT (actually, I've gotten to really hate through-hole, and prefer
surface mount), but BGA is serious voodoo. It's the board layout
equivalent of doing buried vias.

    I first "discovered" Metcals 12+ years ago. I was an software
engineer at a company, and dabbled in hardware. We had a small
manufacturing line with about 6 people on it. Vaugh Equipment Sales
called on us, and somehow wound up talking to me. They came in for a
demo, and brought a Metcal. I was impressed, and became an immediate
advocate. Every company I've worked at has either had Metcals already,
or been converted after some campaigning. There's just no comparison.
I've used the Hakkos, the Wellers, some other brands, and none even come
close to the quality and usability of a Metcal.

    eBay is a great place to find these. Sometimes they go for too
much, and sometimes you can steal one. You want a MX-500, a RM3E wand,
a stand, something like a STTC-025 tip (small "normal" tip, for
through-hole, connectors, etc), a STTC-040 (30 degree angle fine tip,
for SMT), a STTC-117 (similiar to a Weller 100 watt gun tip. Good for
heavy ground planes, etc), and one of the hoof tips for drag soldering
(it's in a box that hasn't been unpacked from the move, can't remember
the number). If you're lucky, and stumble across a Metcal RF Power
Meter for under $100, buy it. It's an in-line wattmeter, and can tell
you a lot about the health of the base, the tip, and your workload.

    I've bought tips off of eBay, too. Find someone selling an
assortment for of 5 or so used tips for $35. So far, everyone I've
dealt with has been accurate and honest about the condition of the
tips. The photos should be up-close and clear.

    The non-MX-500s should generally be avoided. They're getting old,
and if they break, Metcal does not repair them anymore. And trust me,
you CANNOT fix them yourself. They require specialized tuning
equipment. If you repair a Metcal and it gets de-tuned, you'll fry the
output drivers, and it'll be truly dead. Sure, you can fix a power
switch or something like that, but that's not generally what fails.

    The SP-200 should also be avoided. It does not use the same tips as
the MX series, and the output power is about half (15 watts vs 35).
They're not that cost effective to buy, although they're generally
better than something like Weller WTC-201 (or whatever is close to that
number. WT-something).

    Metcal has a good article on why these irons are so good. The tip
temperature is very precise, and because they're low-mass tips, the
respond extremely quickly. They're one of the only irons that are
considered to have "self-cleaning" contacts. For MilSpec work, most
irons require a calibration procedure any time the tip is changed. This
usuallyinvolves cleaning where the tip goes in to the handle, and then
checking it on a temperature measuring device. Because the tip of a
Metcal is basically a section of transmission line, removing it from the
handle cleans the contact area. And last time I checked, Metcal tips
were not required to have a temperature check between changings (but
they do require a weekly test).

    One of the other things I really like about a Metcal is how fast you
can change a tip. A tip heats up to working temperature in about 10-15
seconds. Turning the iron off, you hold the tip against the sponge for
about 10 seconds, and you can remove it with your fingertips. If 10
seconds is too long, a silicon pad comes with a the wand, which allows
you to remove the tip while it's still scorching hot. Also, the wand
cable is silicon, so you don't have to worry about damaging the cable if
you nail it with the iron. They don't, however, take to being slammed
in drawers well (this is the single biggest cause of failure, says
Metcal). The cable is flexible transmission line, and a crimp creates
an impedance bump in the line that causes the iron to be unable to
measure the tip temperature correctly.

    --jc
Received on Sat May 15 2004 - 13:43:48 BST