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Solder Pad Coverage

PCB Process in the Pad Covering Process

PCB soldering is a simple process.

It is the use of a metal called solder to mechanically and electrically connect two metal surfaces. The solder secures the connection so that it will not be loosened by vibration or other mechanical forces. It also provides electrical continuity so that electronic signals can pass through the connection without interruption. A soldering iron is used to melt the solder.

Flux is used to clean and prepare the surface, allowing the molten solder to flow (or "wet") and bond to the metal surface.

Manual soldering is the process of soldering one connection (called a "joint") at a time, as opposed to more automated soldering processes, such as wave soldering (for through-hole assemblies) or reflow soldering (for SMT assemblies).

A. When soldering on a circuit board, the following three factors must be considered:

  1. 1,The size of the solder joint;
  2. 2,The time the soldering iron is in contact with the soldering surface;
  3. 3,The pressure applied to the solder joint with the soldering iron.

B. The size of the solder joint

  1. 1, The size of the solder joint affects the time required for flux activation and solder melting.
  2. 2, Larger solder joints require more heat to melt the solder. Larger solder joints should use a higher wattage soldering iron. In addition, a larger tip should be used on the iron.
  3. 3, The most important thing when choosing a soldering iron head is the amount of thermal connection between the soldering joint and the iron. The thermal connection is the contact area between the soldering joint and the iron.

C. Soldering

  1. 1, After selecting the correct size and shape of the soldering iron tip, you should consider the time of contact between the iron and the solder joint. The correct time for soldering is between 2 and 4 seconds.
  2. 2, This is usually enough time for the flux to activate, the solder to melt and flow into the joint. More or less time will result in poor soldering results. Too little time will result in a cold solder joint, too much time will result in damage to the board and electronic components.

D. Pressure

  1. 1, the soldering iron and the circuit board surface at an angle of 45 degrees and gently apply pressure on the soldering iron as a pen during the soldering process using the soldering iron to apply the level of pressure should only be sufficient to hold the soldering iron in the desired position too much pressure will ultimately lead to the pads and traces on the printed wiring assembly lifting and damage.
  2. 2, in the large soldering joints on the use of too small iron drill bit will occur when the iron is pushed hard to the soldering joints such a situation, and therefore will not be able to melt the solder. This also happens when using a low-power soldering iron. Although a desperate attempt is made to compensate for the lack of heat by applying more pressure to the solder joint with the iron. But it is clear that this is a wrong soldering technique and can lead to damage to the board.

E. Soldering Tools

1, Soldering iron

  1. 1) Select the size and shape of the soldering iron tip that best suits the soldering project. The soldering iron tip should be replaced when the iron is cold and not plugged into a power source.
  2. 2) Soldering iron tips come in a variety of sizes and shapes, and it is easy to replace the tip on a soldering iron. Soldering iron tips can be interchanged to allow the use of the iron in a wider range of soldering applications and for soldering a wider range of different types of components. This flexibility in choosing the shape and size of the soldering iron tip allows technicians to customize the iron for a specific soldering project.
  3. 3) If the soldering iron tip is too small, the solder joint will take much longer to heat up than the preferred time. This can damage circuit boards and temperature-sensitive electronic components.
  4. 4) On the other hand, if the bit is too large, it may burn, lift, or crack conductors and pads on the PCB. It may also damage electronic components. Sometimes the damage is not immediately visible, but later in the operation, the component may work differently than expected, and this thermal damage may also shorten the life of the electronic components.

2, Solder

  1. 1) Solder is a mixture of tin and lead. The most common type of solder is 60/40 (60% tin and 40% ) 63/3763% tin and 37% lead). The solder is the filler material in the solder joint.
  2. 2) When tin and lead are mixed together, the melting temperature of the alloy is lower than the melting temperature of tin or lead. The melting temperature is the point at which the solder changes from a solid to a liquid. For 60/40 solder, the melting temperature is 370F188C). Because of its low melting temperature, the solder melts quickly, thus exposing the component to heat in the shortest possible time.
  3. 3) There are two forms of solder used to solder circuit boards: solder wire and solder paste. Solder wire is coiled on a spool. Solder wires used in electronics range in size from 0.010"-0.050" (0.25mm -1.27 mm).
  4. 4) The shelf life of solder paste is relatively short. The shelf life of solder paste is 3-6 months. If you want to extend the shelf life of solder paste, it must be refrigerated. Solder pastes must be stored in sealed containers. If the solder paste container is opened, it will cause the solder to oxidize.

3, Flux is used to remove oxides from the surface to be soldered.

  1. 1) Fluxes prevent the formation of new oxides during the soldering process. Rosin flux is the most popular type of flux for electronic applications. It is made from extracts of pine sap.
  2. 2) Flux is supplied separately in the form of a pen or paste. Additional flux can be applied to the solder joints and pins or leads of the component if required.
  3. 3) The activation temperature of the flux must be below the melting point of the solder. Flux is usually activated at a much lower temperature than the solder. If the flux does not activate during the soldering process, it indicates a poor solder joint (most likely indicating a cold solder joint).

F. Soldering Procedure

Open the soldering with the correct soldering iron tip installed. Allow the iron to heat up. Most soldering irons can reach operating temperature in less than a minute.

1, Tinning

  1. 1) The soldering iron tip should be tinned before soldering. Tinning is the process of covering a metal surface with a thin layer of solder. If the soldering iron tip is properly tinned and cleaned on a regular basis, it will last longer.
  2. 2) Apply solder to the soldering iron tip when the comfort hopper reaches operating temperature. The soldering iron tip must be hot enough for tinning. It is best to melt a few inches of solder using a thicker wire about 0.050" (1.27 mm) in diameter. The solder dripping from the tip will pick up many oxides and other contaminants.
  3. 3) If the soldering iron tip will not be used for a longer period of time and has a thick oxide layer, the tip should be properly cleaned before tinning. To do this, use a brass wire tip cleaner by inserting the soldering iron tip into a brass wire tip cleaner and twisting it a few times. Never use a steel brush to clean the soldering iron tip instead of the brass wire tip cleaner as it will damage the plating on the tip.
  4. 4) The soldering iron tip should also be tinned after each use. The small amount of solder required for tinning extends the life of the soldering iron tip and saves the cost of replacing the tip.
  5. 5) The surface to be soldered should also be tinned. It improves solderability and prevents surface oxidation during soldering operations.
  6. 6) Tinning should only be started on clean and undamaged surfaces. Tinning must be done before joining the surfaces. After tinning, the surface should be shiny.

2, Solder:

  1. 1) Spread the leads outward so that the component clips to the board, and do not bend the component's leads more than 45°. For passive components such as resistors and capacitors, it is best to cut off the excess leads first for better access to the connectors.
  2. 2) Turn the board over, solder all the leads of a component and cut off the excess wire leads.
  3. 3) On the other hand, for semiconductors such as transistors and diodes, it is best to solder first and then cut off the excess leads. The excess leads take some heat away from the solder joint and prevent thermal damage to the semiconductor components during the soldering process.
  4. 4) It is a good technique to use metal tweezers to hold the leads of temperature sensitive components. If you grab the leads between the solder joint and the body of the component, the tweezers will absorb the excess heat and thus protect the component from thermal damage.
  5. 5) ICs can be soldered directly to the board, but it is best to solder the pins of a Dual In-line Plug (DIP) socket to the board and then place the IC into the socket.
  6. 6) This will prevent thermal damage to the IC during the soldering process. It is also much easier to replace an IC inserted in a socket than to solder the pins directly to the board.
  7. 7) After soldering, all flux residue must be removed to prevent PCB degradation.
  8. 8) If flux residues are left on the PCB, they can cause the board resistance to change, resulting in inaccurate test results.
  9. 9) Flux residues can also cause changes in circuit performance once the PCB is connected to a power source and begins to operate in an electronic device.
  10. 10) Flux residue can be removed in two steps: cleaning and rinsing.
  11. 11) The best way to clean flux residue is to use isopropyl alcohol. Flux residue can also be removed with a flux remover pen.
  12. 12) After removing the flux residue with alcohol, rinse the solder joints in step 2 with distilled water, not tap water. Tap water may leave stains on the PCB because it contains minerals.
  13. 13) After soldering, inspect the solder joints for defects such as cold solder joints, bridging, and solder balls. If any defects are found, repair them immediately. Most bad solder joints can be easily repaired by re-soldering.

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