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Basics of Hand Soldering and PCBA Rework

Hand Soldering is a process to used repair, Modify or conducting joints in a printed circuit board (PCB) assembly process. In hand soldering hot soldering iron tip heats the solder and it flows insides the metallic surfaces to form a solid joint. Mainly hand soldering is recommended in prototyping, Installation, and repairing of PWBs in surface mount technology.

The quality of hand soldering mainly depending on soldering iron tip geometry, Selection of Flex, and instruction followed. Handholding is not so easy to work as normal people think. It is required to adopt some sort of tools and techniques to get minimum scrap rate, higher productivity and better PCBA quality of rework consistency.

Process Control

To rework the printed circuit board assembly with high-quality performance with increased productivity with lower scrap rates a solid process mapping and controlling need to follow. You can also go through and adopt the best practices of benchmarking organizations  

  • Visual Identification Marking of the products that need to Repair: –  The Board that needs to repair must be tagged with a red label so that it can easily be identified and will not mix with good boards. The defective component or section will also identifiable with red arrow stickers so that rework person can directly work on that part without losing productivity.
  • Productivity: – Mapping and controlling the process will lead to increase the productivity and throughput of any production capabilities.it is also helpful to proper man-hour utilization.
  • Scrap Rates: –Improper controlling on Rework Process will directly associate with higher scrap rates. The scrapping of electronic components or PCB assembly means losing the probability of any company.

Selection of tip according to the size of a component

It is very important to choose the size and geometric shape of the solder Iron tip. A Tip must be selected in this way that it will fit the size of the component on the board.

  • Selecting to small solder tip will take a longer time and will not pass heat effectively on metallic surfaces. A Small tip will be too cold and too slow for this operation.
  • If the tip is too Big it will damage the Pad and tip will damage quickly.
  • For fine pitch soldering operations, the long and thin soldering tips are recommended for best performance.
  • Pressing Hard, Rubbing, Scratching the soldering points must be avoided.

Best Hand soldering Procedures

  • Use the lowest possible soldering temperature (when using tin/lead solder not higher than 360°С and when using lead-free solder from 400°С to 425°С).
  • Contact both terminals with heated soldering tip and feed solder wire into the joints. Hold the tip until the melted solder flowed into the joints.
  • Clean the soldering iron tip during its use with special tools (damp sponge, steel brush).
  • Do not apply too much force when soldering (do not apply pressure on a board).
  • The sponge must be damp, not wet. When pressing on a sponge water must not pour around it.
  • Turn off the soldering iron if not in use for 5 minutes or longer.
  • If you finish working with the soldering iron tip, clean it and tin it (apply the coating of solder to the tip).
  • Change a tip properly only by using a rubber pad intended for that purpose.

Defects due to incorrect use of  soldering iron tips

Metal plating tip of soldering iron wears out over the time. Plating life of soldering iron tip on a type of soldering application, types of flux and solder paste used and the soldering skills of the operator. Generally, the manufacturer does not give any guaranty of soldering iron tips. Usage of defective soldering Iron tips results below soldering defects.

  • Cracks: – Due to Excessive pressure is applied with a tip to a contact area resulting in a bend of the tip.it will cause the cracks in the tip coating. To avoid this problem, select the tip that best suit your work.
  • Non-wetting: – Oxidation of tip coating causes heat conductivity reduces due to formed oxides that will not allow proper wetting of molten solder paste. The best remedy to avoid such consequences frequently clean solder tip with a damp sponge, Use the lowest possible temperature, not recommends using active solder flux.
  • Corrosion: –Usage of Active solder paste at high temperature (>450 °C) the coating of the tip can be possible to damage partially or completely. For remedy use less active flux, use clean and damp sponges, and use solder that has RMA flux type.

Important Definitions

  • Conductive heating – heat is transferred from a soldering station (e.g. solder iron) directly to a contact.
  • Convective heating – the transfer of heat through the hot gas or air using hot air device (station).
  • Temperature controlled soldering stations – soldering stations that have fixed working temperature set (the temperature settings are password-protected).
  • Flux – a liquid substance that does not contain any metals and creates good conditions for durable and high-quality soldering results.
  • Modification – the change in the functional characteristics of a product in order to meet new criteria. A modification is usually necessary for introducing structural changes that may be caused by design, drawings, or changes in the layout of components, etc. Modifications can be made only after they have been approved and after receiving product documentation with the detailed description.
  • Repair – restoring the functional characteristics of a faulty detail or product in accordance with applicable drawings and specifications. During a repair, a product is changed to bring the product into conformity with its original functional requirements.
  • Rework – in this process, non-compliant details and products are reworked in such a way as to ensure full conformity with its drawings and specifications.

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