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BiSn solder reflow profile3/19/2024 ![]() 3)įigure 3: TC wires threaded through holes for stress relief Troubleshooting PROBLEM 1: If you are using colored thermocouples purchased from KIC, you will find that you can hang the entire board from two or three of these wires without damaging the attachment or the wire. To keep from accidentally breaking the TC attachments or stressing the solder joint when moving the profiler and the attached board, wrap your TC wires through a hole in the back of the board so that the TC attachment point is never stressed. However, too much solder at the measurement point will increase the heat capacity of the TC and cause your peak temperature measurement to read low. High temperature solder is an efficient heat conductor, so if a tiny bit gets between the TC bead and the lead or pad, you will still get an accurate reading. ![]() To insure accurate readings, it is critical to carefully separate the two wires all the way up to the TC bead after soldering. Your temperature reading will come from the first point of contact between the two wires leading from the TC. This method gives you superior wetting and a stronger solder attachment to the pad or lead. Place the TC bead on the attachment surface and heat both evenly, then touch the solder to the heated TC bead and let the heat from the TC bead melt the solder. When solder has been completely removed, re-scrub the attachment surface to remove any remaining contaminants.Īttachment: Do not attempt to attach the TC by melting solder into the spot and then shoving in the bead. Use as much wick as necessary to remove all free flowing solder droplets. Then place the solder wick on the surface and press the soldering iron into the wick, heating both the wick and the surface to be cleaned. Use alcohol or a suitable solvent to scrub the attachment surface. Surface Preparation: Thoroughly clean your selected TC locations, taking care to remove any residual low temperature solder and other contaminants that might prevent complete high temperature solder wetting. It is also important to place TC’s at the edges of the board and in any areas with small or non-existent components that will heat up faster than the rest of the board. In placing your TC’s, it is important to keep in mind that areas that are densely populated or have larger components will take longer to heat up and also will hold heat longer. The measurements received from these three to twelve TC’s (depending on the size of the board) will allow you to determine whether the thermal profile is consistent throughout the product, and also to measure the heating and cooling profiles of heat sensitive components. Additionally, it is best to place the TC’s so that you receive temperature readings from the hottest and coldest points on the board. TC Locations: TC location is usually determined by identifying critical or sensitive components and attaching the TC’s to the appropriate pads. This will provide a profile that will be very close to actual production conditions and allow you to develop more efficient production recipes. We recommend using a fully populated board for thermal profiling whenever possible. ![]() TC wires can be made from 1′ to 9′ (.3-3 meters) long. The TC Harness eliminates the possibility of plugging thermocouples into the wrong numbered connector.įigure 2: TC harness, available in 9 and 12-channels. If you are attaching 6 thermocouples or more, you may want to use a “TC Harness” with 9 or 12 thermocouples in one connector (see fig. Common, single color, 36 AWG, lower temperature insulation thermocouples can be used, but will often provide sporadic results. These TCs are 30 AWG, have a thick coating of FPA Teflon insulation (260☌), and are colored to reduce the chance of confusing TC locations on the board with the TC number (see fig. KIC sells thermocouples specifically designed for solder reflow and wave solder applications. Required tools and materials are: 10-88-2 high temperature solder, a soldering iron rated above 300☌, a solder wick, and the appropriate thermocouples (TC’s). To complete the operations described in this paper you need to know how to use a soldering iron and solder wick. 10-88-2 solder also creates a solid thermal connection between the TC bead and the temperature measurement point. We recommend 10-88-2 solder for TC attachment because it does not start melting until 268☌, which is above the temperatures the board will see during the reflow process. This Applications Note covers the attachment of thermocouple (TC) wires to a PCB for part profiling using high temperature solder.
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