The Soldering Guide

What do you need to make repairs, where to get it, & who can help.
whiteshadow
Posts: 142
Joined: Mon Jun 01, 2015 1:10 am

The Soldering Guide

Postby whiteshadow » Tue Oct 06, 2015 7:13 pm

Overview

This guide is intended for beginner/intermediate level solderers (although I will cover some advanced topics at the end). Since soldering is part art and part science you will find that everyone has their own personal technique and equipment preferences. The solutions I present here will provide the fastest/easiest/safest way to get good results, and over time as your skill level improves you can adapt the techniques to what works best for you.
I will break the information into three categories; basic, intermediate and advanced. The basic category will cover playfield work, like replacing a diode, lamp or solenoid, the intermediate category will focus on board repair and the advanced category will cover specific advanced board repair techniques like through-hole repair.

Part 1 : soldering/desoldering equipment.
Part 2 : basic (playfield) soldering/desoldering.
Part 3 : intermediate soldering (circuit board).
Part 4 : intermediate desoldering (circuit board).

Soldering tools are not like a wrench set. While a cheap wrench set from Harbor Freight will perform the same as an expensive set, at least initially, there is a vast performance difference between cheap soldering equipment and quality products. On the other hand, beginner/intermediate level solderers aren't going to spend a several hundred to a few thousand dollars on Pace or Metcal so I've attempted to provide high performance, but cost-effective solutions.
Cheap soldering equipment is the number one cause of frustration when people are learning how to solder, so spend the extra money and buy quality tools.
Soldering Irons

Even if you plan on moving on to board repair, it is suggested that you purchase a soldering iron since they are easier to use when working under pinball playfields. Consider getting a 25 watt iron from from a quality manufacturer like Hakko or Weller. Really, nothing higher is needed. The Iron "Tip" is as important as the iron, and this is where a $20 soldering iron really cuts corners (see more info later about Iron "Tips").

The Weller WP25 Professional costs slightly over $40 on Amazon. It comes with a .125" screwdriver Tip (ST3), but some like the ST4 Tip (.187" screwdriver) since it provides better performance for basic soldering tasks. The additional Tip should cost about $8 on Amazon/other.

Hakko discontinued their 25 watt iron that competed with the Weller Pro iron. They now offer a slick adjustable temperature iron (FX-601) at a fair price. When compared to the Weller Pro, it heats up faster and has a faster recovery time (both good, but not critical things for basic soldering). It comes with a .2" screwdriver tip (T19-D5) so if you buy the additional tip for the Weller the price difference is only about $10. Although it could be used for board work in a pinch, a temperature controlled soldering station is the recommended solution (covered in the next post).

The Hakko model, but either one will work fine for playfield work.

Soldering Stations

The first thing you need for intermediate soldering is a good temperature controlled soldering station. Wattage type irons tend to be too hot (after sitting for a while) or too cold (if you solder several joints in a row or the iron can't keep up with the heat dissipation). This is because the wattage is fixed and cannot respond to increased demand. The temperature controlled stations overcome these problems plus you can fine tune the temperature to the job, the tip being used and your personal preferences.
While the FX-601 soldering iron is temperature controlled it does not have the performance of a soldering station. While we're on that topic let's discuss what makes a good soldering station. Two key factors affect the performance of a soldering station: accuracy (how much the temperature swings above and below the set temperature, both at rest and while soldering) and temperature recovery (how fast the tip comes back to temperature when applied to a joint). There are other performance issues directly related to the tip and those will be discussed further on in the thread.
As you look at different soldering stations the first thing you will notice is that cheaper models don't provide any performance data on their product--I presume you can figure out why. So once again you want to go with a quality brand like Weller or Hakko (of course there are other very high-quality brands on the market, but they are much more expensive). I will note though that at the moment Hakko appears to be leading in regards to tip engineering and manufacturing.

One of the dead give-aways on a cheap soldering station (or iron) is that it is not ESD (electro-static discharge) certified. ESD certified products will have a 3-prong AC plug and the soldering tip will be connected to ground. This is an important issue when working on static sensitive devices.
There are two products that I would recommend, with the main differences being price and some minor features. The Weller WESD51 Digital Station costs about $130 on Amazon and the Hakko FX-888D Soldering Station sells for about $90. Hakko also offers a package with the FX-888D and 5 extra tips for about $130 on Amazon. I'll be honest, I like the Hakko products, but either one will get the job done.

In addition to the soldering station and the included tip you will want to purchase some additional tips. In fact tips are the magic that makes one companies product better, or worse, than another. Companies like Weller, Hakko, Metcal and a few others spend millions of dollars each year in R&D attempting to design a better tip. More importantly though, manufacturing a quality tip is not easy, and cannot be replicated by the low cost companies.

Soldering Station Tips

Any high quality soldering station will use tips which consist of four layers. The inner layer of the tip is copper for heat conduction and next is iron, which is the workhorse of the tip. Next out is nickel which is non-wetting, meaning it won't wick the solder away from the tip's working surface. The last layer, chrome, is applied as an additional protective layer.

Weller's graphic:

wellsgardner-soldering-1.png
wellsgardner-soldering-1.png (169.37 KiB) Viewed 2440 times


When selecting a tip you need to consider both shape and size. Many soldering irons come with a conical tip which is just about worthless (IMHO) because it doesn't provide enough surface area for good heat conduction. A much better choice for basic or intermediate soldering is a chisel, or screwdriver, tip.
When sizing a tip, the general rule of thumb is the tip should be two-three times wider than the lead you are soldering, but not wider than the circuit pad. This provides the best combination of tip efficiency (temperature drop, heat transfer, working time and heat storage capacity--see the article below for more info) and minimizing potential damage to the board.
http://www.hakko.com/english/tip_select ... ion_1.html

I typically use chisel tips in the following sizes: .0625", .125" and .187". The smallest tip is for IC's (it won't bridge the gap between leads) and small transistors. The next tip is for larger (driver) transistors and the last is for bridge rectifiers and under-playfield work. You should always size the tip to the job to provide optimum surface contact, good temperature control and avoid overheating sensitive components or traces.
Note: for the image below, the leads are out of proportion (too large) in relation to the pad.

soldering-1.png
soldering-1.png (10.38 KiB) Viewed 2440 times


Note: Most soldering stations require re-calibration when Tips are changed.

For the technical geeks here's a couple of interesting articles. The first covers everything you'll ever want to know about tips and compares the Hakko and Metcal tips. The second covers the performance characteristics of soldering iron tips (in this case Weller, but the theory applies to all brands).

Tip Maintenance

You will need a couple of products to properly maintain your soldering tips. The main concern in tip care is oxidation, which reduces the ability of the tip to transfer heat to the joint. Oxidation is the result of oxygen and the rate of oxidation is increased by heat. It is easier to prevent oxidation than to remove it so some basic preventive care will ensure your tips stay in good shape.
1. Never use an abrasive to clean the tip.
2. Turn the soldering iron/station off when not in use.
3. While soldering, frequently clean the tip using a copper wire sponge (see image below).
4. Tin the tip with a small amount of solder when placed in the stand.
5. Use a wet sponge to clean the tip and apply solder at the end of the day.

In the old days a damp sponge would have been used to clean the tip while soldering, but due to the thermal shock applied to the tip, a copper wire sponge is now the preferred method. The copper is softer than the tip, but harder than the oxidation so it will safely clean the tip. Hakko recommends that at the end of the soldering session you clean the tip using a sponge and the following procedure.
1. lower the temperature to 482 degrees F (soldering stations and adjustable temperature irons).
2. Clean the tip with the damp sponge and inspect the tip.
3. If there is any black oxide on the tip, apply solder with flux and clean again. Repeat until no oxidation remains.
4. Tin the tip with solder.

You will want to use some type of stand for your soldering iron and Hakko sells one that includes the copper wire sponge.

Solder

Solder tends to be a religious issue with everyone having their favorite. I exclusively use Henkel Multicore 63/37 leaded rosin core solder. That doesn't mean it's better than other choices, just that I'm used to how it flows, so why change. Equally important to the brand is the type of solder you use, so let's talk about solder.

The first issue I'll address is lead solder vs lead-free solder. The Restriction of Hazardous Substances (RoHS) directive requires manufacturers to use lead-free solder (technically almost lead-free). Unfortunately there are some downsides to lead-free solder. It requires higher soldering temperatures, is brittle, which leads to solder cracking in high-vibration environments, and does not have the same visual clues that identify a good solder joint as lead solder does. The only downside to lead solder is safety, which we'll discuss later, but when a few simple rules are followed there are no great safety risks with using lead solder.

Manufacturers have been working hard to identify other mixtures that will equal the performance of lead solder, and until they do I'll stick with my leaded.
The next choice is whether you want to use 60/40 Sn/Pb (Tin/Lead) or 63/37 Sn/Pb. The former melts between 361 and 374 degrees while the latter is eutectic since it has a single melting point of 361 degrees. There is some advantage to the latter although it is more expensive.
Solder contains an inner core of flux which cleans the joint and helps the solder flow better. The flux can be either rosin or water-soluble (commonly called no-clean). The former turns acidic when heated so it needs to be removed with a flux cleaner or alcohol after soldering. While technically the no-clean does not have to be removed, solder joints will look more professional (and be easier to inspect) with any leftover flux removed.
The problem with the no-clean fluxes is that they don't clean the joint as well as the rosin core and are actually harder to clean up afterwards. Personally I stick with solder that uses rosin core flux.

The last, and most common mistake I see, is choosing the proper diameter of solder for a specific job. If the diameter is too small it takes forever to feed enough solder to a large joint (coil, for example) and if the diameter is too large it's difficult to flow the solder properly on a small joint (board repair, for example) and not end up with solder blobs. The DoD recommends .031 to .063 diameter solder. I use .031 for circuit board work and .040 - .060 diameter for solenoids, wiring, etc.

As mentioned earlier, I prefer Henkel's Multicore solder. It has 5 strands of flux instead of one and (IMHO) flows better than single core solder. It is more expensive though and a quality single core like the one from Kester or MG Chemicals is an acceptable replacement. Bottom line you want a good quality lead solder with a rosin core flux and a couple of different diameters (one for playfield work and one for board work).

Flux

There are times you will need additional flux in addition to what is provided by the solder. If a joint is heavily oxidized, or you're having trouble getting the solder to flow, adding a little more flux can help. Always use an acid type flux, since it cleans better, and then use a flux remover (MG Chemicals, for example) or alcohol. I have the best luck with hitting it with the flux remover and a toothbrush and then finishing up with alcohol and cotton swabs.
More importantly though is you need flux when desoldering. Think about it, solder has flux in it yet at that point in the process the joint should be relatively clean (since it was protected from oxidation by the solder you just removed). On the other hand, the joint is most oxidized at the point where you are desoldering so why would you not add flux to the mix? I'll discuss flux more once we get into soldering/desoldering, but it really is your best friend and is under-utilized by most people.

Other than quality (I recommend DeoxIT, Kester or MG Chemicals) the main difference in solder flux is the application method. I use a paste that comes in a syringe, but other choices include a rub-on applicator, liquid or a paste you apply with a brush.

Pace makes good products, but as with Metcal they're in a higher price bracket.

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