Choosing the correct solder paste
With so many different types of solder pastes available how can you correctly choose which type of product you should be using?
In order to achieve a reflow profile that fulfills the requirements of the solder paste it is important to understand -
- The evaporation point of the solvents within the paste
- The amount of time for the evaporation to take place
- The point the flux begins to activate and activation time.
This information will be readily available for the solder paste manufacturers and suppliers. The most simple answer is to evaluate what you require form a solder paste itself.
What type of solder alloy? Is it a SAC Alloy, Low Melting Point Lead Free or Leaded? Do residues have to be removed or will your application allow them to remain in place? If the residues have to be removed what will be cleaning process and cleaning solutions used?
What type of stencil life is required and how is the RTP (Response to Pause)? Will the paste be running continuously or will there be interruption? How will the paste be stored? Will it be a refrigerated solder paste or one that is stable at room temperature?
Do you print, print populate and reflow straight away or are their long periods of time allowed to complete the assembly? Is tack time important?
Will voiding cause a potential issue? Gasses generated from the solder paste are trapped in the solder joint creating voids. Some solder pastes are prone to generate higher voiding than others. Newer solder pastes have been formulated with the specific goal to reduce voiding. Our SK P2-5 is a good example of a low voiding, high performance solder paste.
My advise would be to select a solder paste and cleaning process that is suitable for your way of working and application. You can speak to your supplier about changes that may be required to provide the best results.
For help choosing the correct type of solder paste and cleaning solutions for your application please feel free to contact myself or visit solderking.com