Basic Soldering Lesson 1 - "Solder & Flux"

If there is a

basic

task in electronics, one of the most critical skills to master is

solder

ing, for most people,

solder

ing is a very simple thing: a hot iron and some solder, that's it, if we just solder well a couple of tubes. maybe, but soldering printed circuit boards is another matter; Nowadays, welding has reached the level of an art and has become a vital art in many fields. It became a reality with the space age, when incredible amounts of raw energy had to be put into it. under precise electronic control, it all depended on how reliable each of these little soldered connections was.

High reliability is what meant success or failure, and it wasn't just for companies like this, but had been demanded in many other environments, as well as anywhere information was vital. when human lives depended on it and there was no room for failure Roger, a good forty-one thousand today we all depend on and expect high reliability, it's no longer just about very sophisticated systems like this, okay, rack and 178, contact Los Angeles. I don't mean to joke, now we find it everywhere, in the common things we have in the computer systems of companies and government and in all types of consumer goods that incorporate electronic circuits, they become part of our daily lives. and we wait.

To work well with all of them, a

basic

procedure is to make a reliable solder connection and how to do that is what you are about to learn. We will see an expert go over all the basic techniques he needs to know. and then you will have the opportunity to practice them with your own materials. Let me show you what we're going to cover first. We'll take a look at the solder itself, the basic material of the process, and see what's in it. We will also find out about

flux

, what it does and the proper type of use.

We'll cover what really happens when you solder, the meaning of wetting action, and the necessary role

flux

plays in removing oxides and soldering irons. You will learn not only how to match them to the work, but also the many factors besides tip temperature that affect how quickly heat reaches the work, you will learn what WPI means, one of the secrets of true craftsmanship, and you will learn to recognize the good. solder joints and bad ones, what makes them acceptable or unacceptable and what are each of the characteristics of the preferred solder joint, the components we will work with are those that you will find in today's electronics on single and double sided circuit boards with various types of terminals and connection wires after we look at how to solder each of them, you will do so developing professional skills as you go and for your permanent reference we have available a student manual that provides more details on each of the topics.

We're going to cover it, so let's get started and we'll start with the process itself by connecting two pieces of metal together to form a reliable electrical path. Why solder them in the first place? We could attach them with nuts and bolts like this, but later. We have two problems: first, we can't be sure of good contact to begin with and then, the vibration will probably loosen it. Second, oxidation or corrosion will continually occur on the surfaces, progressively decreasing the electrical conduction between the two. a soldered connection eliminates both problems there is no movement and no surface to oxidize we form a continuous conductive path from one to the other what makes this possible are some very unusual properties of the solder itself so let's look at how soldering is made it is an alloy of metal made by combining tin and lead in different proportions here the proportions are equal, so it is known as 50/50 solder 50 percent 10 and 50 percent lead a 60/40 solder would consist of 60 percent tin and 40 percent percent lead.

Find these percentages marked on the various types of solder available and sometimes only the percentage of tin is shown. The surprising fact about solder is its low melting point. Pure lead has a melting point of 620 degrees Fahrenheit. Pure tin has a melting point of 450 degrees, but when you combine them in a 50/50 solder, the melting point drops to 420 degrees lower than either metal alone, and other solder ratios have their own particular melting points. with most combinations, fusion does not occur all at once 50/50 solder begins melts at 361 degrees but does not completely melt until the temperature reaches 420 degrees between these two temperatures solder exists in a plastic or semi-liquid state part but not all has melted the range of plastic is different for other combinations of tin and lead with 60/40 solder, the range is much smaller than for 50/50 and here is a special case, the ratio 6337 known as eutectic solder, has virtually no plastic range and melts almost instantly at 361 degrees, the most commonly used.

The solder in electronics is the 60/40 type, but because of its plastic range, you have to be very careful and not move the wire during cooling, which causes a disturbed joint that looks like this. The weld has an uneven and rough appearance and instead looks dull. Bright and shiny is one of the types of unacceptable joints that we will see in a few minutes. In some circumstances, minimal heat may be desired and it may be difficult to keep cables stable during cooling. This is where eutectic solder is used as it cools. very quickly from a liquid state to a solid state To someone observing the welding process for the first time, it appears that solder simply joins metals together like hot glue, but what actually happens is very different when hot solder comes into contact With the copper surface, a metallic solvent action occurs.

The solder dissolves and penetrates the copper surface. The solder and copper molecules mix to form a new metal alloy that is part copper and part solder with its own characteristics. This solvent action is called wetting action. Wetting can only occur if the surface of the copper is free of dirt and any oxide film that forms when the metal is exposed to air and the solder and working surface must have reached the temperature appropriate. This copper plate looks clean but there is a thin film of oxide that covers it when solder is applied, it acts like a drop of water on an oily surface, the solder does not come into contact with the copper, there is no solvent action and The solder can be easily removed to have a good solder joint.

Oxide should be removed and avoided during the soldering process, as this flux is used when melting, it will remove the thin oxide film, the solder now flows and the wetting action can take place when the metal cools. It is a solid mass that is mechanically and electrically continuous and cannot be scraped off. Many types of flux are available in paste and liquid form. The flux used in electronic work is basically rosin in a modified form and may contain mild activators in some cases to accelerate its action when the flux is cooled, it is relatively non-corrosive and non-conductive, but when heated to its molten state it becomes active enough to remove all surface oxides and remove them during soldering.

Many of the types of fluxes available are acid-based and should never be used for electronic repair they remain corrosive at all temperatures fluxes containing zinc chloride our acidic fluxes and should not be used these fluxes are excellent for their intended use but have not been Resin fluxes for electronic work, although relatively non-corrosive when cold, should still be removed with a solvent after soldering, this prevents their surfaces from becoming sticky. accumulate dirt and moisture. Solder and flux combinations are widely used today. They are available in a variety of solder sizes and flux percentage and have the advantage of automatically controlling the flux to solder ratio.

The concepts we just covered are very important and are presented in their entirety in your manual. At this time your instructor will review the material with you in particular. specifications, standards and practices of your organization and note them in your manual for a permanent record in any type of welding. The main requirement beyond the welding itself is the use of heat. You can apply heat in several ways, but here we are. Mainly concerned with just one of them, the conductive type of soldering iron, these soldering irons come in a variety of sizes and shapes and you must choose the right one for the job at hand.

If we take a look inside the basic soldering iron we would see that there are three main elements. a resistance heating unit the heater block that acts as a heat reservoir and the tip or drill bit to transfer heat to the work on the basic iron the input voltage is fixed and constant so the resulting tip temperature depends on the capacity of the heating unit and in the mass of the tip and block. The more elaborate irons incorporate ways to vary the temperature of the tip in this type, the operator can increase or decrease the voltage across the heater and consequently vary the temperature level of the tip in another type of iron.

Incorporates a temperature controlled magnetic switch within the block The switch is activated by a small magnet When the magnet is attracted to the heater block Close the switch and the iron is heated to a predetermined temperature The magnet loses its magnetic properties and the switch opens Then, as the iron loses heat, the cycle repeats, resulting in a maximum temperature set at the tip. Another variation is this type of iron. A temperature sensor has been built into the block, the operator sets the desired temperature and then, through a closed loop feedback system, the power to the resistance heater is turned off and on to maintain the tip at the desired temperature. .

There are many arguments for and against each of these types of straighteners, but controlling the temperature of the tip is not the real problem. The real problem is controlling the heat cycle of the job. How fast the work heats up How hot it gets and how long it stays there This is affected by many other factors In reality the temperature of the tip is not critical at all The first factor to consider is the relative thermal mass of the joint, Let's start with a single pad and a single-sided board. There is relatively little mass here, so the pad heats up quickly.

If we now move to a double sided board with a pad on both sides of the hole we will have twice the mass we started with, so if we do the hole plating through one we would have an even greater mass and that is before we the component cable between. The mass of the cable can vary greatly. Some cables are much larger than others and that's not all we have to consider in any particular joint, let's say we assemble. a turret terminal here again the mass increases a lot and now we add one or two wires the mass is even greater, each joint has its own thermal mass and how this combined mass compares to the mass of the iron tip determines the temperature increase of work in this situation we have a large work mass and a small iron tip the temperature rise will be slow if we reverse the situation by placing a large iron tip on a small work mass then the temperature rise of the work piece will be faster even though the tip temperature is the same, we could go a step further and consider the capacity of the iron itself, its ability to sustain a given heat flow, let's look again at the basic iron.

Irons are essentially instruments for generating and storing heat and the tank is made up of both. the block and tip the tip is removable and comes in various sizes and shapes it is the pipe so that heat flows to the work for small jobs a tip with a downward neck is used so that only a small flow of heat is produced for jobs large tip is used to provide greater flow, the reservoir is replenished by the heating element, but when an iron with a large tip is used to heat up massive jobs, then the reservoir can lose heat faster than expected. can replenish.

This is where the size of the deposit becomes important. The heating block can sustain a large output flow longer than a small one. Another way to increase the capacity of the iron is to add more heating element and thus increase the power of the iron. These two factors, box size and power determine the recovery rate of the iron, so if the job requires a lot of heat, you not only need the right temperature but also the right tip size, an iron with a capacity Enoughlarge and can recover the relative thermal mass quickly enough, then it is an important consideration for controlling the heat cycle of the job.

A second factor is the surface condition, if the pads and blades are covered with oxides and other contaminants, they create a barrier to heat flow, then even if the iron tip is the right size and temperature, it may can't put enough heat. The joint to melt the solder The tin-iron tip can be kept clean by scrubbing it with a wire brush before each use and then removing any remaining oxides with a damp sponge The work is always cleaned before soldering with a solvent such as trichloroethane or isopropyl alcohol to remove grease or oil remember that you cannot create a good solder joint on a dirty surface after the condition of the surface there is a third factor to consider thermal bond the contact area between the tip of the iron and the work let's see the situation in the cross section with the iron tip touching a round wire, the actual contact occurs only at this point, so the connection area is very small, not much more than a straight line along the wire, we can make things a lot better by putting a small amount of solder here now, the connection area will look more like this and the heat flow will be much faster from the tip of the iron, so now we have seen that there is more to it than just the temperature of the iron tip that affect how quickly the bond will form.

Getting hot has become a complex control problem with a number of variables, each influencing the other and what makes it so critical is time. The general rule of thumb is that for high reliability welds, apply heat for no more than two seconds and you will start to damage the board with all these factors. The welding process seems too complex to control precisely in such a short time, but there is a simple solution for everything and the secret is here WP Workpiece Indicator I When you know how to use workpiece indicators, you know one of the secrets of craftsmanship, simply put, workpiece indicators are the way the work responds to you, the way it tells you what effect it is having and how to control it to achieve what you want The sound is the indicator the workpiece in this job, most often the workpiece indicators are visual and sometimes you can use the sense of touch in any type of work where you are part of a closed loop system begins when you perform some action on the work piece then the work piece reacts to what you felt the change and then modify your action to achieve the result is here in the feeling of the change through sight, sound or touch where work piece indicators work engaged in soldering and desoldering a main workpiece indicator is the recognition of heat rate by observing how fast the heat flows a tip like this is too big and too hot for the job the heating rate is so fast that it does not you can control it this tip is also small for the job what you see is a kind of melt the heating speed is too slow when the correct tip size and temperature are used then the heating speed is correct recognition of the heating speed heat then it is our high reliability welding workpiece indicator makes it complicated The control problem is very simple, just watch and see how long it takes for the solder to melt at the joint, it should melt in two seconds, if it takes Plus, you're increasing your chances of damaging the board.

Damage to the plate comes mainly from heat, but it's not just heat that does it, it's heat combined with pressure. Let's look at a circuit board and pad model. When a hot iron tip is applied with a light touch, there is no damage and it can be done repeatedly, but now if pressure does too. applied this is what happens on the surface the reason can be shown on a graph as the materials are brought to solder fusion temperatures 80 percent of the bond strength between the pad and the plate can be lost in the practice remember not to use more light touch pressure than you would get with the weight of a pencil balanced on its tip, push it down this way and you may lose the pad.

A general rule of thumb to avoid overheating is to get in and out as quickly as you can, that means using the The hottest iron you can react to is one that gives you a one to two second dwell time on the particular joint you are soldering. . In the next part of the program, we will address turret terminals and begin to apply what we now know. High reliability welding