Soldering Tips and Part Replacement

Soldering is an expertise that is a learned skill. I must warn you that the lead in solder is known to cause birth defects. When soldering or handling printed circuit boards, avoid unprotected skin contact with the solder surfaces. Also, while soldering, try not to inhale any solder fumes or smoke. Most electronic distributors have a battery powered air filter available just for this purpose.

General soldering techniques:

• Use a grounded tip, low wattage soldering iron with the right size tip and shape so it will maintain a tip temperature of between 500° to 600° Fahrenheit.
  
  
• Use the proper gauge of rosin core solder composed of 60 parts tin and 40 parts lead.
  
  
• Keep the soldering iron tip clean and well tinned.

Proper soldering techniques.

• Make sure you do not rush the soldering iron heat up time, as the proper temperature is paramount and must be met first.
  
  
• Hold the soldering iron tip and solder against the component lead until the solder melts.
  
  
• Quickly move the soldering iron tip to the junction of the printed circuit board foil and the component lead, and hold it there only long enough for the solder to melt and flow around both the component lead and printed circuit board foil.
  
  
• Work quickly to avoid overheating the circuit board foil or component.
  
  
• Closely inspect your work, and remove any solder bridges with solder braid wick or a static free solder sucker.
  
  
• The solder connection should look shiny and clean, with no brown rosin left behind from the solder, as this can cause ring cracks or a bad connection down the road.
  
  
• Use a small wire brush to clean the printed circuit board and a small spray of non-static, non-residue printed circuit board cleaner.

Unsoldering techniques:

• Touch the soldering iron to the component lead and the printed circuit board landing until the solder melts completely.
  
  
• Quickly draw away the excessive solder away from the component lead and the solder pad on the printed circuit board with an anti-static suction type solder removal device or solder wick braid.

When unsoldering regular types of IC’s, bend the leads to stand up straight at the same time you heat up the solder on the pad and are removing the flowing solder with the solder wick or solder sucker. When you are taking out a bad transistor, diodes and/or resistors,

clip the leads of the component as close to the component body as possible, use a pair of needle noise pliers to grab on to the leads, and heat up the solder to let the cut lead easily come out. Then simply remove the excessive solder.

Some techs will use the remaining leads of the old components as an attachment point for the new component by wrapping the leads of the new components around the old leads and solder those together. In a case as this, double-check the underside of the component leads for a solid good connection. If it looks lose, resolder the connection.

Most surface mounted components are affixed to the printed circuit board with glue. Be careful not to break or damage any foil traces under the components or at the leads of the components while removing. Usually applying heat to the components for a short time while twisting with tweezers will break it loose from the board.

• Chip components must be replaced with identical parts due to critical foil trace spacing.
  
  
• If there are holes under a chip resistor or capacitor, it may be limited to using a 1/8 watt type device.

Chip resistors have a three digit numerical code on them. The first two numbers is the resistance, the third number is the multiplier. If a small chip resistor had a 473 on it, the value would be a 47K, or 47,000 ohms. Chip capacitors generally do not have any values marked on them, and must be identified by the package they come in or from the capacitor designation in the schematic diagram. Chip transistors are identified by a two-letter code. The first letter indicated the type of transistor, and the second letter indicates the grade of that transistor. The manufacture service manual should always be used to properly identify the proper chip components to replace.

Component removal:

• Use solder wick to remove solder from the end caps or terminals of the Component.
  
  
• Without pulling up on the component, carefully twist the component with tweezers to break the adhesive bond between the component and the printed circuit board.
  
  
• Do not re-use removed surface mounted components, as they are subject to stress cracking, and can cause tons of intermittent problems.

Chip component reinstallation:

• Put a small amount of solder on the solder pads on the board.
  
  
• Hold the chip component against the soldering pads with small tweezers, and apply heat to the pads until the solder melts and flows around the end caps or component leads. Do not hold heat to the pads for more then 3 seconds.
  
  
• Always, when resoldering any solder connection, double check your work, and with chip components, use a small magnifying glass to look carefully at the pads.

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