[Fwd: Fwd: "Ask Dr. Solder !" (longish...)]

David V. Rogers dvrogers@bellatlantic.net
Wed, 17 Feb 1999 12:55:16 -0500

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From: Dick Rucker <rrucker@clark.net>
Subject: Fwd: "Ask Dr. Solder !"  (longish...)

>Date: Tue, 16 Feb 1999
>Reply-To: radman@best.com
>Sender: owner-qrp-l@Lehigh.EDU

>From: "Radman" <radman@best.com>
>To: "Low Power Amateur Radio Discussion" <qrp-l@Lehigh.EDU>
>Subject: "Ask Dr. Solder !"  (longish...)

>I received a number of technical questions re: the Weller
>WTCPT solder station and solder tips. Since I'm *not* a
>real "Doctor of Solder," I decided to call one on the
>phone. I had a nice chat with Mr. Larry Smith in Weller's
>engineering support division, and a thirty-year veteran in
>the soldering industry. Here we go with, "Ask Dr. Solder."

>Q: Why is a solder station "better" than a non-temp
>controlled (unregulated) soldering iron?

>A: A non-temp controlled iron *continues* to increase in
>tip temperature the longer it's plugged in -- up to 1100
>degrees-F !

>A solder station controls and maintains an
>exact tip temperature. In the case of 700 degree-F tips,
>you'll be soldering at a tip temperature of 400 degrees
>*less* than a non-temp controlled iron.

>A lower tip temperature with good technique translates to better
>joints with less chance of damage to sensitive components
>-- IC's, etc. (The 700 degree-F Weller tips will *not*
>exceed 710 degrees-F.)

>Q: Which tips do I use -- 700 or 800 degree-F ?

>A: The 700 degree-F tips are typically recommended for
>single layer and double-sided PC boards -- even four-layer
>PC boards. This includes practically everything in the
>world of amateur radio kits & homebrew.

>The most common tip for the WTCPT station is the
>Weller PTA-7 (1/16" screwdriver tip).

>You might also want a PTD-7 for much bigger pads/lugs, and
>a PTJ-7 for longer-reach work -- or <gasp> rework ;)

>If you want to try surface mount, pick up a PTS-7 for a start.
>The 800 degree-F tips are recommended for serious multi-layer
>boards -- 4 to 8 layer PC boards
-- *not* typically used for ham radio kits ;)

>Q: Is the tip of a WTCPT really grounded ?

>A: YES !!! All Weller solder stations have grounded tips.
>You can check the integrity of the tip ground as follows:
>Turn the solder station OFF and let it cool. Pull the plug
>OUT of the AC mains and using your DMM (ohm meter) check
>for continuity between the ground plug on the Weller AC
>plug (you know the one) and the tip of the soldering iron.
>You should be reading approximately one ohm.

>If your  resistance is considerably higher, you probably
>need to clean the tip (with 600 emery cloth, etc) and possibly
>remove the tip and the "barrel" (the hollow part that
>screws the tip to the iron) and clean the threads with a
>brass/bronze brush to remove any oxide build-up.

>Never use a 3-prong to 2-prong "ground cheater plug" --
>obviously, this defeats tip grounding and ESD-safety.

>Q: What is the meaning of "ESD-safe" in soldering stations?

>A: "ESD-safety" guarantees that static energy from your
>body (hands, etc) will be "dumped" to ground via the
>plastic soldering iron handle or solder station plastic
>housing. Otherwise, the ESD would transfer to the
>soldering tip, thus destroying the IC you're soldering.

>The solder station essentially discharges your body's
>static charge to ground every time you pick up the
>soldering iron. (Naturally, you should take additional ESD
>precautions if you're handling *extremely* sensitive
>components -- and not rely on the solder station for all
>ESD-safety in the lab!)

>Q: How long should it take to make a "good" solder joint
>on a common solder pad?

>A: Tricky question! The time spent on the pad is called
>"dwell time." A dwell time of 4 seconds at 700 degrees-F
>might be considered destructive for some components --
>however, a dwell time of 2 seconds with an 1100 degree-F
>unregulated soldering iron can be much more destructive.

>A 700 degree-F dwell time of 3-4 seconds is not uncommon, to
>allow for "filling the pocket" -- that's the volume of the
>thru-plated hole, flush to the component side and properly
>"feathered" evenly to the circumference of the solder pad
>-- on the solder side.

>The "pocket" should be filled -- but not over-filled --
>and the solder in the center of the pad should rise evenly
>to the component lead that will be trimmed.

>Never have a solder pad with an under-filled
>"dimple" on the pad. The solder level at the component
>lead should be higher than the edges of the pad.

>A soldered pad should never look like a "round BLOB of
>solder *sitting* on the pad." Wire soldering is more of an
>art than a science, and with practice -- 1 to 3 second
>dwell times can be achieved, while safely meeting all of
>the above criteria.

>Q: What about residual flux that's left on the board?

>A: Flux removal is an issue that's best answered by the
>solder and board manufacturer. However, the *color* of the
>flux -- after soldering a pad -- is a good indicator of
>whether your dwell time is too long.

>Your residual flux should look "honey-colored" rather
>than "caramel colored."  If you're starting to burn the
>flux, your dwell time is too long, OR your tip temp is
>too high, OR you need to consider a different tip shape,
>OR applying heat to the pad/component lead from a different

>Heat primarily the pad, and catch the lead with the side
>of the tip -- then practice, practice... practice.
>Have a friend time you and inspect your work if you're serious.

>Q: Any closing remarks?

>A: Soldering stations allow for greater soldering
>consistency when compared to non-temp controlled irons.
>Overall, this translates to fewer cold joints, fewer
>heat-damaged components and fewer heat-damaged pads and
>traces. The quality of your work will be superior,
>compared to soldering with non-temp controlled irons.
>Remember to wash your hands after you're finished handling
>solder. Never smoke cigarettes or eat while soldering.
>Never allow kids to play with solder. And, practice
>soldering! It's still an art -- not a science!

>There you have it! A conversation with "Dr. Solder."
>Happy soldering,
>Conrad Weiss - NN6CW

Richard A. "Dick" Rucker
City of Fairfax, VA