Hand Soldering Wires to a Starboard or a COB

When hand soldering wires to a metal core printed circuit board, such as a typical starboard used for rapid prototyping, certain precautions and techniques are recommended to avoid damage to the solder pads or LED. Soldering wires to metal core printed circuit boards (MCPCB) can be challenging due to their inherent ability to dissipate heat. Figure 1 below shows a typical starboard with an LED on it. This article discusses attaching wires to a starboard after the LED is mounted using a standard SMT reflow process.

Figure 1:  LED on Starboard

Figure 2 shows an example of a suitable soldering station. Temperature control and adjustable tip size are essential for good results.

Figure 2: Temperature-Controlled Solder Station

Figure 3 and 4 show examples of soldering wires. It is important to avoid using excessively long stripped sections of wire since they may short out something when assembled (Fig 4). Smaller wires are easier to reflow. We recommend using the smallest wire gage that can carry the intended current. An AWG calculator can be found in “Electrical - Wire Gauge Calculators”. It is also easier to solder using small solder wire diameters. Small diameter SAC305 no-clean flux core solder wire is commonly used.

Figure 3.  strip wire to the proper length and tin wire and solder pad

Figure 4.  Soldering wires to PCB

Below are some recommendations for achieving the best results when hand-soldering wires to starboards.

1. 1. Use no clean solder flux and small diameter solder wire.
   2. Make sure the surface you are soldering to is clean and free of any dust, dirt, or anything.
   3. Use a non-thermally conductive surface (such as a piece of wood ) under the starboard that can handle high temperatures. Do not try soldering to starboards mounted on a heatsink.
   4. Pre-tin solder pads.
   5. Pre-tin the wires.
   6. Use a soldering iron that is temperature-controlled and has thermal feedback to keep the soldering tip at a constant temperature while soldering. See the example in Figure 2.  There are many brands like Hakko, Metcal, and JBC.
   7. Select the right tip to match the size of the surface you are trying to solder to.
   8. Practice on a blank starboard or spare part if possible.
   9. During handling, make sure not to contact the LED.
   10. Never touch the surface of the LED under heightened temperature. Allow the starboard to come to room temperature before handling.
   11. Follow electrostatic discharge procedures to prevent damaging any ESD sensitive components on the printed circuit board.
   12. Do not leave the soldering iron tip on the starboard for long periods of time. Leaving the soldering iron on the starboard for an extended period of time can damage the device and lift the soldering pads.
   13. If cleaning the solder joint is required, isopropyl alcohol can be used. Take care not to touch or use any cleaning device on the lens of the LED.
   14. After soldering, do not handle by just picking up the wire. This could cause the solder pads to delaminate.

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