Imprint © 2011 Franzis Verlag GmbH, 85586 Poing www.elo-web.de Author: Thomas Riegler and Burkhard Kainka ISBN 978-3-645-10062-5 Produced on the order of Conrad Electronic SE, Klaus-Conrad-Straße 1, D92240 Hirschau/Germany. All rights reserved, including the rights of photo-mechanical reproduction and storage in electronic media.
Table of Contents 1 Introduction 5 2 Components 6 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 6 6 7 7 8 9 10 11 3 4 Battery Resistors Ceramics Capacitator Electrolyte Capacitator LED Transistor Diode Integrated Circuit (IC) Soldering Basics 12 3.1 3.2 3.3 3.4 3.5 3.6 12 12 13 16 17 18 What is Soldering? The Soldering Iron Soldering Equipment Too Hot and too Cold Solder Points The Right Tools Before Starting Soldering Soldering 19 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.
.13 4.14 4.15 4.16 4.17 4.18 4.19 4.
1 Introduction Specialist trade offers innumerable electronics circuit construction kits that you can solder together yourself. If you want to work with them, you should know how to handle a soldering iron. This learning package helps discovering the secrets of soldering step by step. In a series of subsequent exercises, you will learn how to solder various components and how to develop and build complete circuits.
2 Components 2.1 Battery The battery must be connected to any circuit in the correct polarity. The required battery clip has a red (plus) and black (minus) connection wire each. Both wires must be soldered on according to the required polarity. Figure 1: Battery circuit symbol 2.2 Resistors Resistors are some of the simplest electronic components. They are labelled in a colour code consisting of three rings and to be read from the edge to the centre.
Figure 3: Resistor Figure 4: Resistor circuit symbol 2.3 Ceramics Capacitator The capacitator is another important electronics component. It is available in two versions. The simpler version is the small, round and flat ceramics capacitator. It is secured against polarity reversal. Capacities are indicated in Farad (F). The ceramics capacitator is labelled in a number code. 104 corresponds to 10 x 104, i.e. 100,000 Picofarad (pF).
Figure 7: Electrolyte capacitator circuit symbol Figure 8: The electrolyte capacitator must be installed in the correct polarity. 2.5 LED Always observe polarity when installing a light diode. The LED has two connection wires of different lengths. The longer one is the plus pole. It is called anode (A). The minus pole, the cathode (K), has the shorter wire. The polarities are also visible inside the LED. The minus pole has the shape of a large triangle. The plus pole is only very small.
Figure 9: An LED must be installed in the correct polarity. Figure 10: LED circuit symbol 2.6 Transistor The transistor amplifies small currents. Its connections are called emitter (E), basis (B) and collector (C). The cylindrical casing is flattened on one side. The type designation is printed on here. Looking at the transistor so that the connections point down and the label can be read, the emitter is on the left side. The basis is at the centre. Figure 11: Transistor with view of the flattened side.
Figure 12: NPN transistor circuit symbol 2.7 Diode A diode lets current through in one direction only and blocks it in the counter-direction. It can be imagined like a check valve from a water installation. Conventional diodes are cylindrical like resistors. Their minus pole (cathode) is marked with a dash. SMD diodes are very small. They are labelled on top with a short designation consisting of a letter and a number. The left end of the label marks the cathode (–), the right one the anode (+).
Figure 14: MD diodes are very small. 2.8 Integrated Circuit (IC) The learning package contains an IC type LM358 in SMD build. The installation direction must be observed when soldering on the IC. Polarity reversal must be avoided. It may destroy the component. PIN 1 is marked by a point at the top of the casing. Figure 15: PIN assignment of the SMD-IC LM358 Figure 16: At the SMD-IC, PIN 1 is marked by a point at the top of the casing.
3 Soldering Basics 3.1 What is Soldering? In electrical engineering, soldering is one of the basic ways of establishing connections. Soldering creates an electrically conductive connection that cannot be disconnected. Using a melted metal binding agent (solder), soldering connects two metal work-pieces e.g. a PCB onto which an electrical component is soldered. The solder has a lower melting point than the metals to be connected. Soldering is performed at temperatures of around 340 °C.
Universal soldering iron Universal soldering irons are slightly larger. Their power consumption is between 20 and 40 W. They are particularly suitable for hobby and craft use. They can also be used well for electronics soldering. They are also the first choice if you want to assemble simple to medium electronics kits. Standard soldering iron Standard soldering irons consume about 50 to 150 W and are already too large for electronics hobbyists and handicrafts enthusiasts. They have an angled soldering tip.
The solder sponge is one of the most important, as well as the most simple accessories of the soldering iron. It is moistened with water and placed in the intended dish of the soldering iron holder. Then you can clean the soldering tip by wiping off contaminations or excess solder. A fine mechanics’ clamp makes soldering easier. It can hold the PCB and keep it in the position where work is easiest for you. This will leave your hands free for the soldering iron and solder.
Figure 18: Stable soldering iron stand with solder sponge for cleaning contaminated soldering tips Figure 19: The fine mechanics’ clamp can be used to hold and comfortably solder PCBs. Figure 20: Soldering aids with magnifying glasses also hold the PCB.
Figure 21: De-soldering pump (order no.: 588502-62) to remove excessive solder 3.4 Too Hot and too Cold Solder Points Perfect soldering can be recognised by its nice gloss. A cold soldering point looks somewhat matte and often has a lumpy surface. Defective solder points can also be recognised if the small solder cone around the component connection is missing or hardly there. Cold solder points have only low mechanical resistance.
Figure 22: Correct solder points are glossy with a smooth surface. 3.5 The Right Tools Soldering is best done with suitable equipment. We recommend the 15-W solder iron starter set available from Conrad Electronic (order: no.: 588292-62). In addition to a 15-W soldering iron, it comprises two soldering tips, solder, a deposit stand and a de-soldering pump. If you only need the soldering iron, we recommend the 15-W hand soldering iron, also available from Conrad Electronic (order no.
Figure 23: Starter solder sets (Order no.: 588292-62) contain everything one needs to learn how to solder. 3.6 Before Starting Soldering Proper soldering is only possible if you keep the soldering tip clean at all times. Regularly wipe it off with a moist sponge. This removes excess solder from the soldering tip. Figure 24: Over time, solder collects at the soldering tip, which makes soldering considerably more difficult.
4 Soldering 4.1 Tinning Stranded Wire Fine-stranded wires are hard to solder because their strands go in all directions when soldering. The battery clip wire ends show how perfectly tinned wires should look. Cut off the tinned parts and strip about 5 mm of the wires. Then twist the strands evenly between your fingers. This makes the wire more stable. Heat one wire end with the soldering iron and add a little solder. Heating melts the solder immediately and covers the wire piece with a solder film.
4.2 Soldering Together Wires For both wires to keep their position during soldering and you to have both hands free to work, clamp them into an electronics clamp and put them in position. Then use the soldering tip to heat both wire ends evenly. Now add the solder by moving it to the heated solder point. This solder process also should be completed quickly to keep the wire from heating up too much and the insulation from being damaged.
Practice first by bending wire pieces with a few millimetres stripped of insulation on either end. Figure 29: The wire bent to shape with an electrician’s round pliers. Figure 30: For electrical components, the wires should not be bent right at the casing end. 4.4 Soldering Wire Bridges to Strip Grid There are two types of universal PCBs for constructing self-developed circuits, already applied with the copper layer required for soldering.
The lateral strip grid made up of 19 fields is well suitable for first exercises. You can solder on wire bridges and later components just by placing connection wires on the top half of the contact areas. Place the PCB and the wire bridge on the work surface. Strip a wire bridge end and align it with one of the contact surfaces. Then heat the wire and the solder point with the soldering iron tip and add a little solder. Ensure that there is no connection with the adjacent soldering areas.
Figure 31: Soldering wire bridges to the lateral strip grid 4.5 Soldering Wire Bridges to a Point Grid If you solder wire bridges to a point grid, push the wire ends to be soldered together through the bores of the hole grid part of the test PCB. Observe that there is only a small metal ring around each bore. It is isolated against the adjacent ones. This is called a land. There is not a lot of space for placing the solder to prevent conductive connections to the adjacent lands.
Figure 32: Soldering iron and solder must be moved precisely onto the land. Soldering should only take a few seconds. 4.6 Soldering Wire Bridges to a Point Grid - Version 2 The PCBs included in the learning package are coated on one side, like in most soldering kits. The components are pushed through from the bottom. Only the long connection wires of the components or the ends of the wire bridges will point out of the lands then.
Figure 33: To prevent the components pushed through from below from falling out during soldering, bend the connection wires slightly to the side. Figure 34: The PCB is turned around for soldering. 4.7 De-soldering Lateral Wire Bridges De-soldering must be practised. Again, the soldering iron must be heated to operating temperature. Start with the wire bridges soldered to the lateral strip grids in exercise 4. Clamp the PCB into the electronics clamp.
When de-soldering, make sure not to touch any adjacent solder points or components with the hot soldering iron. Keep the de-soldering process short. The wire end should be de-soldered within 5 seconds. Figure 35: Pull slightly on the wire with your fingers while heating the soldering area, until the wire comes loose. 4.8 De-soldering Soldered-In Wire Bridges Proceed according to exercise 4.7. The difference is merely that you need to work precisely.
Figure 36: Pull slightly on the wire during heating in this version as well. 4.9 Simple LED Circuit: Preparations For your first circuit, your circuit plan only requires soldering on the battery clip, a resistor and a diode. In spite of the circuit being simple, the first question is how to transfer it to the PCB. A simple sketch helps with this. We decide building the circuit at the lateral strip grid. Since every strip also has two bores, the components can be soldered on to it going to the side.
Figure 37: Simple LED circuit diagram Figure 38: Transfer the circuit diagram to a small sketch to see where and how to solder on the individual components. 4.10 Simple LED Circuit Use the soldering sketch from before to start soldering. Start with the resistor. It is a resilient component and can be handled like a wire bridge. After soldering on the resistor on both ends, solder the diode anode to the strip grid right at the resistor.
ode to one of the adjacent strips. When soldering, observe that the lower bores of the strip grid segments remain free. Push the red plus line of the battery clip through the bore of the strip to which the left resistor connection is soldered. Push the black minus wire into the free bore of the segment to which the LED cathode is soldered. Solder on both wires. Now all you need is a connection between the resistor and LED anode. Solder in a wire bridge here.
Figure 40: Push the wires of the battery clips through the still-free bores at the two outer contact surfaces and solder them on. Figure 41: Last, solder the connection between resistor and LED with lots of solder.
During your first de-soldering exercises, you will have noticed that some residual solder remains at the solder point after de-soldering of a component or wire bridge. Is usually collects in the bore, so that no connection wires can be pushed through anymore. This is where the de-soldering pump comes in. Tension it first. For this, push down the sliding piston until it catches.
Figure 43: After using the de-solder pump once, the solder bridge is removed. 4.11 Soldering SMD Diode SMD means „surface mounted device“. SMD components usually have no wire connections but are soldered right to the PCB. they are also very small. The SMD diode 1N4148 included in the soldering course is only 3 mm long, including lateral connections. Their component body is even only approx. 1.5 mm long. The brief designation printed on the top is used to determine polarity.
Place the SMD diode on the installation area with pincers and continue to hold it while fixating it with a soldering iron. For this, heat the diode at the side with the pre-tinned pad for a second. Now the SMD diode is soldered on on one side. Last, solder the second diode end as already known. Again, soldering should not exceed one second. Figure 44: First, tin a pad with a little solder. Figure 45: The SMD diode is very small even under a magnifying glass.
Figure 46: Keep the SMD diode in place with pincers while heating the pre-tinned pad and the diode connection resting on it. Figure 47: Last, solder on the second end by adding a little solder. 4.12 Soldering SMD Operational Amplifier SMD-ICs like the operational amplifier LM358 are soldered similarly to small SMD diodes. It is a little easier because they are slightly larger. First, pre-tin an IC field pad with a little solder.
pincers so that its connections are located precisely on the contact surfaces. Keeping the IC in position with the pincers, heat the connection on the pre-tinned pad. Now the SMDIC is attached. Solder on the other connections in sequence by placing the soldering tip precisely and adding a little solder. Ensure that no conductive connection to the adjacent soldering areas is created. Clean the soldering tip thoroughly after each soldering process by wiping it at the moistened sponge.
Figure 49: Pre-tin a pad first. Figure 50: Every connection must be soldered on individually.
4.13 Soldering Components Close Together This exercise starts the step-by-step construction of a transistor circuit. If you install all components in the last required position from the first, you will reach a completed circuit step by step. Sometimes, individual components must be soldered close together or their connections require soldering them in directly adjacent bores or lands. Since there is little space, the soldering tip and solder must be placed precisely.
Figure 52: Working form the centre to the edge makes it easy to solder in components close together. Figure 53: Keep a calm hand to solder on higher components (like this LED) to directly adjacent lands.
4.14 Soldering Sensitive Components Transistors and ICs are sensitive components that must not be heated for long. They would be destroyed by it. Soldering must be performed quickly and precisely for this. The faster you can solder a pin on sensitive components, the less thermal load is placed on them. Soldering should be finished within 2-3 seconds. When installing a transistor or IC, ensure correct installation position.
4.15 Removing Short Circuits Caused in Soldering When soldering points and components, conductor paths, etc. are close together, it is possible that a conductive connection is created by the solder during soldering. The circuit is not destroyed by this. You can still repair the circuit by removing the excess solder. The easiest way of removing it depends on amount and position. The de-soldering pump will help in most cases.
Figure 57: Solder lumps can be removed by heating them and applying the de-soldering pump. Figure 58: Here, solder short-circuits two strip grids. There is only little solder. It can be removed with the soldering iron.
Figure 59: The last residue can be scratched off with a small electronics screwdriver or a needle. 4.16 Completing Transistor Circuit After soldering the resistors, LEDs and the transistor to the PCB, all you need now is the battery clip, some wire bridges and a switch. Form the latter from two wire pieces that are only soldered onto the circuit at one end. strip the free ends a little. Touch them to each other to close the switch.
Figure 60: The finished circuit 4.17 Checking Circuit and Shortening Excessive Lengths Before taking the circuit into operation, check by way of visual inspection that all components are correctly installed and that no solder points were forgotten. Now shorten the excess lengths of the component connection wires with an electronics wire cutter. Leave about 1 mm of excess length at the back of the PCB.
Figure 61: Excess connection wire lengths must be cut off after completing and inspecting the circuit. Figure 62: The cut connections should protrude over the PCB by 0.5 to 1 mm. Figure 63: Cut off the connection wires closely to the solder cones. 4.18 De-soldering Components with Several Legs Simple components like wire bridges or resistors can be de-soldered easily. This becomes more difficult when a component like a transistor has several connections close together.
First, heat one of the solder points for the three transistor connections, and keep the desoldering pump ready at the work-site. Once the solder has liquefied, trigger the pump to remove part of the solder. Repeat this process until the bore is solder-free. Then take on the other two connections. In the end, all three bores should be free and you can simply pull the transistor from the PCB. LED and IC can be de-soldered the same way. Figure 64: Multi-legged components cannot be de-soldered easily.
Figure 66: The de-soldering pump removes the solder completely from all three solder points in several goes. 4.19 The Masterpiece Build your own light-sensitive circuit according to the following circuit diagram. This circuit will let you practice everything you learned in this soldering course. This includes transferring the circuit to the PCB, installing LEDs, transistor, SMD-IC and SMD diode correctly and soldering correctly. You also need to install a few wire bridges.
Figure 67: Light-sensitive switch circuit diagram Figure 68: The finished circuit should look about like this. 4.20 Other Circuits The components in the soldering learning package permit soldering a great number of other circuits as well, such as most circuits of the Conrad-Electronic advent calendars from the years of 2008, 2009 and 2010. You can download the circuit templates from http://www.elo-web.de/ergaenzungen.
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