DVD-61C Splicing Wires - IPC Training Home Page

DVD-61C TranscriptIt takes some practice to properly strip wire using these types of tools. There are some hand toolsand methods – such as the use of Exacto knives, razor blades and wire cutters – that are definitelynot acceptable for mechanical stripping.Another effective tool for manually stripping insulation is a thermal stripper. After the thermalstripper melts or softens the insulation, you can use your fingers to twist off the insulation slug inthe direction of the wire lay. Most thermal strippers are adjustable. Always use the lowest heatsetting to minimize damage to the insulation or wire. Do not remove the insulation slug with thethermal strippers. Using the tool to pull off the insulation slug can potentially damage thearrangement 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 usedproperly, thermal strippers produce a perfect strip every time. The main disadvantage of thermalstrippers is that some insulation, such as PVC, will burn and release hazardous gasses whenmelted. If you’re not sure which types of insulation are appropriate for thermal stripping, be sureto ask your supervisor.Sometimes the conductor strands will have a slight discoloration from thermal stripping. Thiscondition may be acceptable – per IPC standards. It’s not acceptable when the insulation isburned 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 tothe conductor strands or the insulation. It’s important that the original lay of conductor strands berestored -- whenever it is disturbed by stripping. That’s because wire separation, or birdcagingcan change the diameter of the wire.A strip may be rejected if there’s any damage to the conductor. When there are nicks or cutstrands on the conductor, it indicates that an improper technique has been used. Depending onwhere the wire is used and the amount of damage, it may be acceptable for a wire to have one ormore nicked or broken strands. The IPC A-610, J-STD-001, and 620 documents provideacceptance criteria for the maximum allowable nicked or broken strands -- based on the totalnumber of strands in the wire.For wires that are going to be soldered, there is typically a final wire preparation step. Thesewires 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 -- coatedwith solder; or move the tip of a soldering iron that is coated with solder over a stationary wire; ordip 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 ofelectronic equipment. This equipment typically contains circuit board assemblies and othersensitive electronic devices. One of the biggest causes of electronic failure -- when makingcircuit repairs – is electrostatic discharge, or ESD. ESD occurs when static electricity from yourbody is discharged into an electronic component. This electricity can degrade or destroy thefunctionality of certain types of components.2

DVD-61C TranscriptThere are a wide variety of materials and techniques to eliminate the build up and discharge ofstatic electricity. Refer to IPC-DVD-54C for detailed information on ESD Control. The generalprinciples 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 theworkstation. These grounding wires will capture any built up electrical charges and conduct themharmlessly into the ground. It’s also important to make sure that your wrist straps and shoegrounders are operating properly -- by testing them often.Unfortunately, we don’t always have the luxury of this degree of ESD protection. We can’talways be at an ESD safe technician's bench – especially when we’re working in the field. Forthese situations, it’s important to utilize a portable ESD field service kit. The kit typicallyconsists of several connection points for wrist straps; a grounding wire that is usually connectedby an alligator clip to an unpainted metal grounding point inside the equipment chassis; and astatic dissipative work surface that allows an ESD safe resting place for sensitive components andcircuit boards.The last topic in this introductory section is safety. Enclosure panels and other metal hardwaremay 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 areused improperly.Soldered SplicesNow, let’s examine soldered splices. There are four different types of soldered splices. Theseare mesh, wrap, hook and lap. There is no one best splice. Each type of splice has advantagesand disadvantages. Factors that need to be considered include available slack, requiredclearances, and required strength.For example, if you are making a repair inside a chassis or assembly, you don’t always have theluxury of lots of slack or extra wire to work with. In addition, you may have to pull thecompleted splice through a small panel opening. Under these conditions, you would need tomake 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 otherelectronic repairs. Always follow proper lock-out tag-out procedures. It’s a good idea to test thewires inside the existing chassis with a voltmeter to verify they are not “live.” And make sureyou’re wearing ESD grounding equipment.Let’s start by examining the mesh splice. A meshed splice is one where the strands of wireinterlace, or interconnect evenly and are of equal length. These splices use the least amount ofwire.3

DVD-61C TranscriptThe first step is to strip both the wires. The insulation that we remove should typically exposethree to five wire diameters of the stranded wire. It’s important to note that the mesh splice is theonly 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 toplace the heat shrink tubing onto one side of the splice BEFORE you make the splice and start thesoldering, and keep it enough “upstream” to be away from the heat source. Also, make sure thatthe length of the tubing will cover the insulation on both ends of the splice - plus a minimum ofthree 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 thestrands interlace evenly and are of equal length. Twist the wires slowly to restore the original layof the wire. It’s important to avoid over twisting. Let’s watch how it’s done one more time -- soyou can better understand what’s involved. Notice that conductor strands are smoothlyinterlocked 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 recommendedstarting point, which may need to be adjusted based upon tip selection, wire size and the type ofsolder being used. First we select a soldering iron tip. Generally a medium chisel tip is veryeffective.Now, we solder the connection. Add just enough solder so it can penetrate the splice area, butleave the outline of the strands visible. At this point, we clean the soldered splice if cleaning isrequired. Then we inspect it. An acceptable mesh splice is where the solder is wetted to bothwires -- 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. Thenapply 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 theheat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; orif the tubing doesn’t overlap the wire insulation on both ends for a minimum of three wirediameters.Now, let’s take a look at the wrap splice. Wrap splices require a longer amount of wire tocomplete 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 goodsplice.Now we're ready to place the heat shrink tubing onto the wire. Make sure that the length of thetubing is sufficient to extend over the wire’s insulation -- on both sides of the spliced area – adistance of three times the wire insulation diameter. After shrinking, the tubing’s inside diametershould allow a snug, firm fit over the wire insulation.4

DVD-61C TranscriptNow, we’ll make the wrap splice. The first step is to position the wires in an “X” pattern. Thensecure one wire firmly and begin the wrap motion of the opposite wire until one turn iscompleted. Perform the same step with the remaining wire – by firmly securing it and wrappingit in the opposite direction. With one wrap completed in each direction, you can finish thewrapping 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 thatcould extend beyond the outer circumference of the wrap. A wire protrusion that extends beyondthe splice may cause damage to the insulation or tubing – possibly resulting in a short circuit. Asyou can see, the proper wrap splice interlocks the two wires smoothly -- for a minimum of threewraps.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 youcan 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 weapply 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 theheat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; orif the tubing doesn’t overlap the wire insulation on both ends -- for a minimum of three wirediameters.Now, we’ll examine the hook splice. A hook splice is similar to a wrap splice in that the splicetakes up a lot of space. The wires are first stripped and then pre-tinned in the same manner as thewrap 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 onewire 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 theopposite direction.With one wrap completed in each direction, you can finish the wrapping process to obtain thethree wrap minimum requirement. Now, we’ll cut any remaining wire flush to the wrap. As youcan 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, butleave the outline of the strands visible. At this point, we clean the soldered splice. Then weinspect it. An acceptable hook splice is where the solder is wetted to both wires and you can stillsee the outline of the wire strands underneath the solder.To complete the hook splice, we position heat shrink tubing over the spliced area. Then applysufficient heat to shrink the tubing to a snug fit over the splice and the wire insulation.5

DVD-61C TranscriptThe hook splice is considered defective if there are any sharp points or projections covered by theheat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; orif the tubing doesn’t overlap the wire insulation on both ends for a minimum of three wirediameters.The final soldered splice we’ll be explaining is the lap splice. The lap splice can be used to jointwo or more wires. The first step is to strip the wires. Each wire end should have the samelength of insulation removed so that they appear identical. Each wire end should be stripped aminimum 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. Theyshould 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 asimilar type clamp. When using alligator clips, consider placing a small folded piece of businesscard or a thick heat shrink between the clips and the wire insulation to avoid “teeth marks” in thewire.Now, we’ll be wrapping the positioned wires. Use a wire that is about equal in diameter to asingle strand of the wires being spliced. For example, if you’re splicing two 24 AWG wirestogether, 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 thenfold the wire to tin the middle part. If the wire has been tin plated, it’s important to clean itbefore wrapping. Try to minimize handling during the wrapping process so that oils from yourfingers 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, butleave the outline of the strands visible. Notice that the completed solder connection may have aslightly convex fillet along the length of the connection, as long as the individual wire used tosecure 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 iswhere the solder is wetted to the wires and you can see the outline of the wire strands underneaththe solder.To complete the lap splice, we position heat shrink tubing over the spliced area. Then apply heatto 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 theheat shrink tubing; if the conductor strands pierce the tubing; if the wire splice area is exposed; orif the tubing doesn’t overlap the wire insulation on both ends for a minimum of three wirediameters.6

DVD-61C TranscriptNow that you know how to make the four types of soldered splices, let's take a look at anotheroption. This involves the use of a heat shrinkable solder device where a solder preform is insidethe heat shrink tubing. Stripped wires are purposefully NOT pre-tinned, per J-STD-001. Once thestripped wires to be spliced are inserted into the heat shrinkable solder device, external hot air isapplied and the solder preform achieves a molten state. Notice that the heat shrink tubing alsoshrinks into a snug fit over the splice and insulation, and in many devices a ring of glue meltsinside each end to hermetically seal the solder joint.Crimped SplicesNow, 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 uponthe size of the wires to be spliced, we’ll select the proper terminal and crimping tool. Forcrimped 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 metalbarrel. 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 thewires to be spliced. Stripped wires are never tinned for crimping operations. Then we pre-loadthe terminal barrel into the crimper nest. The stripped wires are now positioned inside theterminal 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 theratcheting mechanism – also referred to as a full cycle tool – these crimpers will not release untilthe 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 wirestrands. This funnel reduces the possibility that a sharp edge on the terminal will cut or nick thewire strands.The crimp should be centered and properly formed in order to retain the wires. It’s important toverify that the barrel splice is not cracked and that the wires cannot be pulled out when applyingmoderate pressure.An acceptable barrel crimp can tolerate some variation from our target crimp. For example, therecan be some insulation gap – meaning the insulation doesn’t have to be exactly flush against thebarrel splice – as long it is within two wire diameters. The bare wire end can also be less thanflush, but is visible within the crimp indentation. In addition, the crimp can be slightly off center-- as long as it is properly formed.7

DVD-61C TranscriptThe barrel crimp is considered defective if the insulation gap exceeds two wire diameters; if theconductors extend more than two wire diameters beyond the crimp barrel; if the wire insulationextends into the barrel splice crimp; if the barrel splice is cracked; or the crimp indentation is offthe end of the barrel and the bellmouth is not evident; when the wires are not contained in thecrimp; or if the conductors were twisted together or pre-tinned before they were inserted into theterminal.Now, let’s watch how double sided crimped splices are made. As you can see, the crimpingprocess 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 verifythat the ends of the wires are visible inside the terminal. Make sure that you can see eachconductor in the inspection window. The criteria for double sided splices are similar to barrelsplices.Ultrasonic Weld SplicesThe 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 isenough heat generated to bond, or weld the wires into a splice, or nugget. Ultrasonic welding ismore effective on bare copper wires than on tin coated wires. The advantage of ultrasonicwelding 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 correctamount of insulation from the wires. Since ultrasonic welding machines are typically used forhigh volume applications, we use an automated machine to cut and strip wire from a reel. Thestripped wires should be long enough so that only bare wires are visible in the tooling area of theultrasonic 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 areusually inserted on the bottom. Smaller wires are loaded on top of the larger wires. Themaximum height should not be greater than the meeting point of the anvil and the insert. Incorrectpositioning 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 isdone using the menu selections on the control panel of the ultrasonic welding machine. The weldparameters are typically called up by splice numbers, sequence numbers, or by scanning barcodes for each type of splice.Once the correct weld parameters are set up, we can start making the splices. Let’s watch thisprocess 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 wirediameters from the weld nugget.8

DVD-61C TranscriptDefective insulation clearance occurs when insulation is inside the weld nugget; or the insulationgap is so large that the conductor violates minimum electrical spacing; or when the end of theinsulation is less than one wire diameter, or is more than two wire diameters from the weldnugget.Now, let’s turn our attention to the weld nugget. A target weld nugget has a width to height ratioof 1.5 to 1 – meaning the width is 50% longer than the height. The individual wire strands are notdistinguishable on the top and bottom of the nugget. An acceptable weld nugget has a width toheight ratio of at least 1 to 1, but does not exceed 2 to 1. And it’s acceptable when individualwire 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 whennugget 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 preparationprocess. Then we examined the four types of soldered spices – mesh, wrap, hook and lap. Wealso described crimped splices -- and splices made on ultrasonic welding machines.Each method of splicing wires has advantages and disadvantages. It’s important to use theappropriate splice for the required application. If you have any questions about which spliceworks best for a given situation, ask your supervisor.The quality of a single splice can affect the operation of an entire electronic product. It isabsolutely 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