DVD-61C Splicing Wires

Transcription

1 DVD-61C Splicing Wires Below is a copy of the narration for DVD-61C. The contents for this script were developed by a review group of industry experts and were based on the best available knowledge at the time of development. The narration may be helpful for translation and technical reference. Copyright IPC Association Connecting Electronics Industries. All Rights Reserved. Introduction In this video we ll be describing the different methods of splicing wires. Wire splicing is used when it s difficult to replace the entire length of a damaged wire. However, the first choice should always be the replacement of the entire wire when possible. Using splices to repair broken or damaged conductors is not permitted for Class 2 and 3 products without customer approval. Wire splicing may also be a necessary technique for original production assembly, in a customer design to replace terminal blocks when the space is limited, or when the design revision changes. Spliced wires may be secured by soldering, by crimping or by ultrasonic welding. We ll be examining the techniques for making wire splices, as well as the advantages and disadvantages of each procedure. We ll also be discussing the criteria used for determining the acceptability of a particular splice, and we'll be describing various defective conditions. Before we explain the details of wire splicing, let s review the wire preparation process. The first step in any manual wire preparation is cutting the wire to size. We start by snipping the defective portion of the wire that needs to be spliced with an approved cutting tool. Next, select the same size wire, carefully measure the length that needs to be replaced and cut the wire to size. There are two methods you can use to remove insulation from the ends of the wire mechanical strippers and thermal strippers. Each of these methods has advantages and disadvantages. Generally, the end product and the available tools at your company will determine which method you ll use. There are two types of mechanical strippers double jaw and standard mechanical. The wire is placed in the appropriate diameter hole at the specified strip length. The handles of the tool are then closed and the insulation is stripped. The procedure is similar for the standard mechanical strippers. The difference is the technique used to remove the insulation. The goal is a wire with a clean insulation cut of 90 degrees. 1

2 It takes some practice to properly strip wire using these types of tools. There are some hand tools and methods such as the use of Exacto knives, razor blades and wire cutters that are definitely not acceptable for mechanical stripping. Another effective tool for manually stripping insulation is a thermal stripper. After the thermal stripper melts or softens the insulation, you can use your fingers to twist off the insulation slug in the direction of the wire lay. Most thermal strippers are adjustable. Always use the lowest heat setting to minimize damage to the insulation or wire. Do not remove the insulation slug with the thermal strippers. Using the tool to pull off the insulation slug can potentially damage the arrangement or lay of the wire strands and the stripper blades. The advantage of thermal strippers is that they never nick or scrape the wire. When used properly, thermal strippers produce a perfect strip every time. The main disadvantage of thermal strippers is that some insulation, such as PVC, will burn and release hazardous gasses when melted. If you re not sure which types of insulation are appropriate for thermal stripping, be sure to ask your supervisor. Sometimes the conductor strands will have a slight discoloration from thermal stripping. This condition may be acceptable per IPC standards. It s not acceptable when the insulation is burned or charred; or if the insulation is ragged; or if there s not a clean cut. Now, we ll take a look at strip criteria. The preferred strip is when there is no visible damage to the conductor strands or the insulation. It s important that the original lay of conductor strands be restored -- whenever it is disturbed by stripping. That s because wire separation, or birdcaging can change the diameter of the wire. A strip may be rejected if there s any damage to the conductor. When there are nicks or cut strands on the conductor, it indicates that an improper technique has been used. Depending on where the wire is used and the amount of damage, it may be acceptable for a wire to have one or more nicked or broken strands. The IPC A-610, J-STD-001, and 620 documents provide acceptance criteria for the maximum allowable nicked or broken strands -- based on the total number of strands in the wire. For wires that are going to be soldered, there is typically a final wire preparation step. These wires will need to be tinned. Tinning ensures that when the wire is bent -- it won t be damaged. It also prevents birdcaging and improves solderability. There are several ways to tin a wire. We can move the wire across a soldering iron tip -- coated with solder; or move the tip of a soldering iron that is coated with solder over a stationary wire; or dip the wire in a solder pot. The majority of the wires that you ll be splicing will be in the cabinets of an existing chassis of electronic equipment. This equipment typically contains circuit board assemblies and other sensitive electronic devices. One of the biggest causes of electronic failure -- when making circuit repairs is electrostatic discharge, or ESD. ESD occurs when static electricity from your body is discharged into an electronic component. This electricity can degrade or destroy the functionality of certain types of components. 2

3 There are a wide variety of materials and techniques to eliminate the build up and discharge of static electricity. Refer to IPC-DVD-54C for detailed information on ESD Control. The general principles of ESD prevention however, are easy to remember. Always be sure that your body, your workplace and the workpiece are at the same electrical potential by properly grounding the workstation. These grounding wires will capture any built up electrical charges and conduct them harmlessly into the ground. It s also important to make sure that your wrist straps and shoe grounders are operating properly -- by testing them often. Unfortunately, we don t always have the luxury of this degree of ESD protection. We can t always be at an ESD safe technician's bench especially when we re working in the field. For these situations, it s important to utilize a portable ESD field service kit. The kit typically consists of several connection points for wrist straps; a grounding wire that is usually connected by an alligator clip to an unpainted metal grounding point inside the equipment chassis; and a static dissipative work surface that allows an ESD safe resting place for sensitive components and circuit boards. The last topic in this introductory section is safety. Enclosure panels and other metal hardware may have sharp edges or burrs. You ll need to take care when handling this equipment. Also, keep in mind that all the hand tools you ll be using have the potential to injure you if they are used improperly. Soldered Splices Now, let s examine soldered splices. There are four different types of soldered splices. These are mesh, wrap, hook and lap. There is no one best splice. Each type of splice has advantages and disadvantages. Factors that need to be considered include available slack, required clearances, and required strength. For example, if you are making a repair inside a chassis or assembly, you don t always have the luxury of lots of slack or extra wire to work with. In addition, you may have to pull the completed splice through a small panel opening. Under these conditions, you would need to make a small profile splice -- since a larger profile splice would not fit through the opening. Other considerations in determining what splice to use include your company s standards, customer requirements and the purpose of the splice. It s important to never work on live or powered up equipment when performing splicing or other electronic repairs. Always follow proper lock-out tag-out procedures. It s a good idea to test the wires inside the existing chassis with a voltmeter to verify they are not live. And make sure you re wearing ESD grounding equipment. Let s start by examining the mesh splice. A meshed splice is one where the strands of wire interlace, or interconnect evenly and are of equal length. These splices use the least amount of wire. 3

4 The first step is to strip both the wires. The insulation that we remove should typically expose three to five wire diameters of the stranded wire. It s important to note that the mesh splice is the only soldered splice where you won t be pre-tinning the wires. If you are creating the splice inside a chassis, without access to one of the wire ends, be sure to place the heat shrink tubing onto one side of the splice BEFORE you make the splice and start the soldering, and keep it enough upstream to be away from the heat source. Also, make sure that the length of the tubing will cover the insulation on both ends of the splice - plus a minimum of three wire insulation diameters. Now, form the mesh splice by fanning the wire strands on both un-tinned wires into a cone shape. Gently begin meshing the wires together a minimum of 1.3cm, or one half inch so that the strands interlace evenly and are of equal length. Twist the wires slowly to restore the original lay of the wire. It s important to avoid over twisting. Let s watch how it s done one more time -- so you can better understand what s involved. Notice that conductor strands are smoothly interlocked for a minimum of three, but not more than five wire diameters. Once you are satisfied with the splice, it can be soldered. 260 degrees C is a recommended starting point, which may need to be adjusted based upon tip selection, wire size and the type of solder being used. First we select a soldering iron tip. Generally a medium chisel tip is very effective. Now, we solder the connection. Add just enough solder so it can penetrate the splice area, but leave the outline of the strands visible. At this point, we clean the soldered splice if cleaning is required. Then we inspect it. An acceptable mesh splice is where the solder is wetted to both wires -- and you can still see the outline of the wire strands underneath the solder. To complete the mesh splice, we position the heat shrink tubing over the spliced area. Then apply heat to shrink the tubing to a snug fit -- over the splice and the wire insulation. The mesh splice is considered defective if there are any sharp points or projections covered by the heat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; or if the tubing doesn t overlap the wire insulation on both ends for a minimum of three wire diameters. Now, let s take a look at the wrap splice. Wrap splices require a longer amount of wire to complete the splice. The wire should be stripped to allow a minimum of three wraps not twists of each wire around each other. After stripping the wires, they should be tinned. Generally, using a solder pot creates a thinner, more uniform coating. A thick coating of tinning will make it more difficult to form a good splice. Now we're ready to place the heat shrink tubing onto the wire. Make sure that the length of the tubing is sufficient to extend over the wire s insulation -- on both sides of the spliced area a distance of three times the wire insulation diameter. After shrinking, the tubing s inside diameter should allow a snug, firm fit over the wire insulation. 4

5 Now, we ll make the wrap splice. The first step is to position the wires in an X pattern. Then secure one wire firmly and begin the wrap motion of the opposite wire until one turn is completed. Perform the same step with the remaining wire by firmly securing it and wrapping it in the opposite direction. With one wrap completed in each direction, you can finish the wrapping process to obtain the three wrap minimum requirement. Now, we ll cut any remaining wire flush to the wrap. This will eliminate any wire protrusion that could extend beyond the outer circumference of the wrap. A wire protrusion that extends beyond the splice may cause damage to the insulation or tubing possibly resulting in a short circuit. As you can see, the proper wrap splice interlocks the two wires smoothly -- for a minimum of three wraps. Now we can solder the connection. Add just enough solder so it can penetrate the splice area, but leave the outline of the strands visible. At this point, we clean the freshly soldered splice. Then we inspect it. An acceptable wrap splice is where the solder is wetted to both wires and you can see the outline of the wire strands underneath the solder. To complete the wrap splice, we position the heat shrink tubing over the spliced area. Then we apply enough heat to shrink the tubing to a snug fit -- over the splice and the wire insulation. The wrap splice is considered defective if there are any sharp points or projections covered by the heat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; or if the tubing doesn t overlap the wire insulation on both ends -- for a minimum of three wire diameters. Now, we ll examine the hook splice. A hook splice is similar to a wrap splice in that the splice takes up a lot of space. The wires are first stripped and then pre-tinned in the same manner as the wrap splice. Next, we place the heat shrink tubing onto the wire. Now, we re ready to make the splice. We start by forming a 180 degree bend in each wire making sure that the tinned wire strands do not separate during this process. Then secure one wire firmly and begin the wrap motion of the opposite wire -- until one full turn is completed. Perform the same step with the remaining wire by firmly securing it and wrapping in the opposite direction. With one wrap completed in each direction, you can finish the wrapping process to obtain the three wrap minimum requirement. Now, we ll cut any remaining wire flush to the wrap. As you can see, the proper hook splice interlocks the two wires smoothly for a minimum of three wraps. Now, we solder the connection. Add just enough solder so it can penetrate the splice area, but leave the outline of the strands visible. At this point, we clean the soldered splice. Then we inspect it. An acceptable hook splice is where the solder is wetted to both wires and you can still see the outline of the wire strands underneath the solder. To complete the hook splice, we position heat shrink tubing over the spliced area. Then apply sufficient heat to shrink the tubing to a snug fit over the splice and the wire insulation. 5

6 The hook splice is considered defective if there are any sharp points or projections covered by the heat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; or if the tubing doesn t overlap the wire insulation on both ends for a minimum of three wire diameters. The final soldered splice we ll be explaining is the lap splice. The lap splice can be used to join two or more wires. The first step is to strip the wires. Each wire end should have the same length of insulation removed so that they appear identical. Each wire end should be stripped a minimum of four wire diameters. Then we tin the stripped wires. Now, we place the heat shrink tubing onto the wire. At this point, we line up the wires. They should be positioned so that the tinned lengths of wire overlap and are touching each other. Notice that the end of the first wire butts against the ends of the insulation of the second wire. If a flat surface is not available the wires may be secured in position with alligator clips or a similar type clamp. When using alligator clips, consider placing a small folded piece of business card or a thick heat shrink between the clips and the wire insulation to avoid teeth marks in the wire. Now, we ll be wrapping the positioned wires. Use a wire that is about equal in diameter to a single strand of the wires being spliced. For example, if you re splicing two 24 AWG wires together, a piece of solid 30 AWG wire would be a good choice. We recommend tinning the wrapping wire. Notice that we tin one end, then the other and then fold the wire to tin the middle part. If the wire has been tin plated, it s important to clean it before wrapping. Try to minimize handling during the wrapping process so that oils from your fingers don t contaminate the wire and interfere with the soldering process. Now, we'll solder the connection. Add just enough solder so it can penetrate the splice area, but leave the outline of the strands visible. Notice that the completed solder connection may have a slightly convex fillet along the length of the connection, as long as the individual wire used to secure the spliced wires is clearly visible in the solder. At this point, we clean the freshly soldered splice. Then we inspect it. An acceptable lap splice is where the solder is wetted to the wires and you can see the outline of the wire strands underneath the solder. To complete the lap splice, we position heat shrink tubing over the spliced area. Then apply heat to shrink the tubing to a snug fit -- over the splice and the wire insulation. The lap splice is considered defective if there are any sharp points or projections covered by the heat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; or if the tubing doesn t overlap the wire insulation on both ends for a minimum of three wire diameters. 6

7 Now that you know how to make the four types of soldered splices, let's take a look at another option. This involves the use of a heat shrinkable solder device where a solder preform is inside the heat shrink tubing. Stripped wires are purposefully NOT pre-tinned, per J-STD-001. Once the stripped wires to be spliced are inserted into the heat shrinkable solder device, external hot air is applied and the solder preform achieves a molten state. Notice that the heat shrink tubing also shrinks into a snug fit over the splice and insulation, and in many devices a ring of glue melts inside each end to hermetically seal the solder joint. Crimped Splices Now, let s turn our attention to crimping. Crimping is an alternate method of splicing wires. The advantage to crimping is that it's a quick and solderless technique for splicing wires. There are two types of crimped splices a barrel splice and a double-sided splice. Based upon the size of the wires to be spliced, we ll select the proper terminal and crimping tool. For crimped splices to be reliable, it s important to match the wire size, terminal and crimping tool. In terms of strip length, the copper conductor should be in the crimp zone, half way into the metal barrel. The insulation should be just inside the funnel -- with no copper conductor exposed. Terminal manufacturers may also provide specific instructions regarding strip lengths. We ll begin by making a barrel splice. The first step is to strip insulation from the ends of the wires to be spliced. Stripped wires are never tinned for crimping operations. Then we pre-load the terminal barrel into the crimper nest. The stripped wires are now positioned inside the terminal barrel. The wire insulation should be flush against the end of the barrel on both sides. The last step is to close the handles of the crimping tool to complete the crimp. Because of the ratcheting mechanism also referred to as a full cycle tool these crimpers will not release until the crimper is fully closed. Now we ll inspect the crimp. Notice that the wire insulation is flush against the barrel splice. The bare wire ends should also be flush with the barrel splice and the bellmouth is evident. The bellmouth is the flare that's formed on the edge of the crimp and acts as a funnel for the wire strands. This funnel reduces the possibility that a sharp edge on the terminal will cut or nick the wire strands. The crimp should be centered and properly formed in order to retain the wires. It s important to verify that the barrel splice is not cracked and that the wires cannot be pulled out when applying moderate pressure. An acceptable barrel crimp can tolerate some variation from our target crimp. For example, there can be some insulation gap meaning the insulation doesn t have to be exactly flush against the barrel splice as long it is within two wire diameters. The bare wire end can also be less than flush, but is visible within the crimp indentation. In addition, the crimp can be slightly off center -- as long as it is properly formed. 7

8 The barrel crimp is considered defective if the insulation gap exceeds two wire diameters; if the conductors extend more than two wire diameters beyond the crimp barrel; if the wire insulation extends into the barrel splice crimp; if the barrel splice is cracked; or the crimp indentation is off the end of the barrel and the bellmouth is not evident; when the wires are not contained in the crimp; or if the conductors were twisted together or pre-tinned before they were inserted into the terminal. Now, let s watch how double sided crimped splices are made. As you can see, the crimping process is the same. We re just using a different type of terminal and crimping tool. Notice that both sides of the terminal are crimped and that there is an inspection window to verify that the ends of the wires are visible inside the terminal. Make sure that you can see each conductor in the inspection window. The criteria for double sided splices are similar to barrel splices. Ultrasonic Weld Splices The last method of wire splicing is ultrasonic welding. This technique uses a welding machine. The way it works is that high frequency sound is applied to two or more wires being spliced. This ultrasonic sound creates molecular movement and heat in the copper wires. There is enough heat generated to bond, or weld the wires into a splice, or nugget. Ultrasonic welding is more effective on bare copper wires than on tin coated wires. The advantage of ultrasonic welding is that it is a quick and solderless method of splicing wires. Now, let s take a look at the ultrasonic welding process. The first step is to strip the correct amount of insulation from the wires. Since ultrasonic welding machines are typically used for high volume applications, we use an automated machine to cut and strip wire from a reel. The stripped wires should be long enough so that only bare wires are visible in the tooling area of the ultrasonic welding machine. We don t want the insulation to be part of the weld nugget. The next step is to insert the wires into the tooling area. Wires with the largest cross section are usually inserted on the bottom. Smaller wires are loaded on top of the larger wires. The maximum height should not be greater than the meeting point of the anvil and the insert. Incorrect positioning typically results in a splice that doesn t have the desired strength. At this point, we can call up the correct weld parameters for the specific splicing job. This is done using the menu selections on the control panel of the ultrasonic welding machine. The weld parameters are typically called up by splice numbers, sequence numbers, or by scanning bar codes for each type of splice. Once the correct weld parameters are set up, we can start making the splices. Let s watch this process for a moment so you can see how it works. Now, we inspect the weld. We ll be looking at the insulation clearance and the weld nugget. An acceptable insulation clearance is where the end of the insulation is between one and two wire diameters from the weld nugget. 8

9 Defective insulation clearance occurs when insulation is inside the weld nugget; or the insulation gap is so large that the conductor violates minimum electrical spacing; or when the end of the insulation is less than one wire diameter, or is more than two wire diameters from the weld nugget. Now, let s turn our attention to the weld nugget. A target weld nugget has a width to height ratio of 1.5 to 1 meaning the width is 50% longer than the height. The individual wire strands are not distinguishable on the top and bottom of the nugget. An acceptable weld nugget has a width to height ratio of at least 1 to 1, but does not exceed 2 to 1. And it s acceptable when individual wire strands are distinguishable on the top and bottom and there are no loose strands. A defective weld nugget is indicated by any loose wires; discoloration of the conductors; or when nugget width to height ratio is less than 1 to 1, or exceeds 2 to 1. This program has presented the details of wire splicing. First, we reviewed the wire preparation process. Then we examined the four types of soldered spices mesh, wrap, hook and lap. We also described crimped splices -- and splices made on ultrasonic welding machines. Each method of splicing wires has advantages and disadvantages. It s important to use the appropriate splice for the required application. If you have any questions about which splice works best for a given situation, ask your supervisor. The quality of a single splice can affect the operation of an entire electronic product. It is absolutely vital, with each type of connection, to match the right wire, connector and tools. People s lives may depend on these connections being done right -- and lasting a long time. 9