Comments on solder joints when repairing photographic equipment

Flawless, nice, solder joints are usually also good quality solder joints.

Lead-containing solder then shines silvery and lies thickly around the components to be connected.

Such solder joints should last a long time.

This can be achieved ideally on new, clean circuit boards and similar components, where there is enough space for soldering and the soldering process can be repeated with new material if necessary.




Soldering joints are not always as easily accessible as shown here.

The two solderings on the red cables are original „nice“ soldering points that were placed during production.


Difficult soldering conditions

The situation is different for cameras or motor drives that are close to the age of the grizzled repairman.

Soldering points are often difficult to access; they are located in angled housings, adjacent to heat-sensitive parts, especially cables and their thin insulation.

If cables have to be stripped and extended, tensile problems often arise and solder joints can then break in inaccessible places.




Here approx. 1.5 cm had to be soldered in a narrow cable shaft.

The new soldering point - see arrow - is not „pretty“ but serves its purpose, which can be recognized by the silvery shimmering lead-containing solder.


Due to their age, such soldering joints are sometimes fragile; a short pull on a cable can be enough to break the connection.

As a rule, you will find multi-core, fine cables that can be easily bent and laid in small spaces.

Such cables are not always easy to solder because they do not tolerate heat well. The wires often cannot be twisted before soldering because they are difficult to access and then dissolve in the liquid solder.




This switch had to be removed so that its solder connections could be accessed.


Old soldering joints are not always easy to heat with the soldering tip. Here flux helps to liquify the old solder.


Summarized

• Soldering in photo equipment is often done under less than ideal conditions.
• Therefore, „form follows function“ and, as already noted, a good solder joint is always a „nice“ one.
• But even less attractive soldering joints can serve their purpose. In many cases better soldering is not possible due to the circumstances.

Are you just wondering …

… why the original soldering is almost always flawless and beautiful?

The answer is simple:

These solder joints were either made during production, e.g. of a circuit board, or in a condition that had not yet been installed. For example, cable harnesses were laid and soldered before additional parts were installed.

As a repairman, you are almost always confronted with „given facts“ and have to make the best of them.

Often you only have one attempt.


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All information provided without guarantee and use at your own risk.

Two common causes of poor solder joints are:

- heating the solder rather than the part to be soldered. Ideally one heats the connectors just enough, and the solder flows onto them. Melting solder with the iron but onto a cold connector will cause a poor solder joint.

- physically disturbing the joint before it has cooled enough to solidify. The cooling is usually very quick, but if you are holding the wires in place with your hands, sometimes even a tiny shake is enough to disturb the joint.

As you mention, in repair it is often difficult to gain enough access to re-solder under ideal conditions. Additionally, the original assemblers probably had a jig to hold the parts in exactly the right place. Lacking ideal conditions, using a "helping hands" device (these usually have two alligator clips and a magnifying glass) to hold the work in place, leaving your hands free for the iron and solder wire, can help.

Use a solder sucker or braid to draw the old solder away

Clean with fresh flux

Connect the joint or support the wires so that they will not move as the solder cools

So not use an overly hot/large soldering iron - this is the #1 cause of small solder surface damage

Heat the joint, not the solder, and flow the solder into the heated joint

Let is cool completely before moving anything.

Tin both surfaces to be joined and then simply "sweat" them together. Use only a minimum of flux (none if it can be avoided) and wash off any excess flux once the joint has cooled as flux is usually acidic and will eat away at fine PBC tracks and the strands of fine wires causing more problems in the future.
Steve

Steve Roberts said:

… and wash off any excess flux once the joint has cooled as flux is usually acidic and will eat away at fine PBC tracks and the strands of fine wires causing more problems in the future.

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No clean flux/solder should prevent this?

Use:

• Clean the area
• Use clean flux
• Use only rosin core flux, never acid core
• If the solder joint is not shiny, then it is probably a cold joint. Reheat the joint until it stays shiny.

Sometimes old wires must be replaced, because the metal may be dull, discolored, and all but impossible to solder.

TBH, those factory solder connections in the first photo look a bit cold and underfluxed, since the solder does not flow all the way around the pad on the board, but beads up around the wire.

I would recommend the use of a good 63/37 rosin flux core solder for electronics. Pine rosin used as flux is non-corrosive and its presence will not degrade electronics, but I would still clean it off as best practice. I would never use a corrosive acid based flux on electronics.

A 63/37 solder (that is a solder made of 63% tin and 37% lead) is desirable because as opposed to other ratios, 63/37 is eutectic meaning it bypasses the semi-solid state going directly from liquid to solid, which prevents the cold joint created by disturbing it while cooling that reddesert mentions.

Another great thread. I've not had reason to do much soldering in my 60 years bouncing around this planet. I've done some here and there while fixing things but never as a profession. I've been putting time into gaining the skills needed to work on some of the later generation cameras and have come up with a few rules that probably apply to my circumstance only. One rule is that I don't try to solder anything before noon. With the morning coffee, come the essential tremors that make any delicate work by hand a very difficult thing to accomplish. These settle out by noon though. Another for me is to have lots of light on the subject and clean readers, or better, the magnifier hood on.

Seeing what I need to work on and a steady hand is a prerequisite for aging hands and eyes.

Sirius Glass said:

Use only rosin core flux, never acid core

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You probably mean rosin core solder. This works well, although the rosin stains are usually difficult or even impossible to remove. Fortunately, they're mostly harmless. If clean work is desired, use a more modern flux-core solder and clean remaining flux with something like IPA or ethanol. Rosin also has the habit of carbonizing and fouling the tip and soldered parts, preventing a good solder joint, but a cleaning pad for the solder tip should be kept at hand anyway, so it's not a major issue.

koraks said:

You probably mean rosin core solder. This works well, although the rosin stains are usually difficult or even impossible to remove. Fortunately, they're mostly harmless. If clean work is desired, use a more modern flux-core solder and clean remaining flux with something like IPA or ethanol. Rosin also has the habit of carbonizing and fouling the tip and soldered parts, preventing a good solder joint, but a cleaning pad for the solder tip should be kept at hand anyway, so it's not a major issue.

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Where and what should I buy a modern flux? I have plenty of solder, if I'm replacing a component on a PCB it's so easy because the spot is tinned. I have mixed success with rosin for flux.
I can sweat copper plumbing perfectly, key is always clean and flux.

Rosin in principle works well, but burns easily. After a few seconds, it's gone and what remains is just carbonized muck that gets in the way of your work. It works, but there are good reasons why other kinds of flux appeared on the marketplace.

Really, any kind of colorless flux intended for electronics work is OK. Doesn't have to be fancy; I use generic cheap Chinese flux and it does the job just fine, and cleans easily. If you prefer you could also purchase from mouser, amazon etc. etc. The main difference in flux from a practical viewpoint is its viscosity. The flux I use the most has the consistency of vaseline (in fact, it looks exactly like it!), which I apply locally with a toothpick or so. I also have the somewhat thinner kind that squirts from a syringe; it's somewhere halfway between a paste and a liquid in terms of consistency. There's also properly liquid flux that is nearly watery in consistency, which you also dispense using a syringe. All variants work.

Don't use flux intended for e.g. copper pipe soldering etc. for electronics. These are too corrosive.

mshchem said:

I can sweat copper plumbing perfectly

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Yeah. I can do a fair job as well, although I generally have an excess droplet of tin, so it's not perfect aesthetically, but technically I can do a good job. I still vastly prefer soldered joints for copper pipe over clamp fittings etc. Soldered joints are space-efficient and when you get it right (which isn't hard), it's an absolutely perfect seal and you don't have to put any mechanical stress on the pipe, and you don't need any specific tools either. A torch and some sandpaper go a long way.

koraks said:

You probably mean rosin core solder. This works well, although the rosin stains are usually difficult or even impossible to remove. Fortunately, they're mostly harmless. If clean work is desired, use a more modern flux-core solder and clean remaining flux with something like IPA or ethanol. Rosin also has the habit of carbonizing and fouling the tip and soldered parts, preventing a good solder joint, but a cleaning pad for the solder tip should be kept at hand anyway, so it's not a major issue.

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I was taught right out of Electrical Engineering school to have a damp sponge to regularly wipe the zip of the soldering iron to keep the solder and flux as clean as possible.

Yeah, that works well. I do the same.