Selective soldering
Encyclopedia
Selective soldering is the process of selectively soldering
components to printed circuit boards, molded modules, etc. that could be damaged by the heat of a reflow oven
in a traditional SMT
assembly process. Consequently this process usually follows an SMT oven reflow process, but not always. Therefore parts to be selectively soldered are most often surrounded by parts that have been previously soldered in a surface mount reflow process, and the selective solder process must be sufficiently precise in order to avoid these components so as not to damage them.
There are other selective solder applications that can be considered, some of which are non-electronic such as lead-frame attachment to ceramic substrates, coil-lead attachment, SMT attachment such as LED
s to PCBs, fire sprinklers where the fuse is low temperature solder alloys and many more.
Regardless of selective soldering equipment used, there are two types of selective flux applicators: a spray fluxer and/or a dropjet fluxer. The spray fluxer applies atomized flux to a specific area, while the dropjet fluxer is more precise, and the choice depends on the circumstances surrounding the soldering application.
Soldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...
components to printed circuit boards, molded modules, etc. that could be damaged by the heat of a reflow oven
Reflow oven
A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards .- Infrared and convection ovens :...
in a traditional SMT
Surface-mount technology
Surface mount technology is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards . An electronic device so made is called a surface mount device...
assembly process. Consequently this process usually follows an SMT oven reflow process, but not always. Therefore parts to be selectively soldered are most often surrounded by parts that have been previously soldered in a surface mount reflow process, and the selective solder process must be sufficiently precise in order to avoid these components so as not to damage them.
Process
There is a number of assembly processes used to perform selective soldering; these include:- Selective aperture tooling over wave solder. These tools effectively mask off the areas previously soldered in the SMT reflow soldering process while exposing only those areas to be selectively soldered in the apertures of the tool. The tool/PCB assembly is then passed over traditional wave soldering equipment to complete the process. Each tool is specific to a PCBPrinted circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
assembly. - Mass-Selective-Dip-Solder fountain, is the analog of selective aperture, whereby specialized tooling with apertures to allow solder to be pumped through it represent the areas to be soldered. The PCB is then presented over the selective solder fountain and all selective soldering of the printed circuit board are soldered simultaneously as the PCB is lowered into the solder fountain. Each tool is specific to a PCB assembly.
- Miniature wave selective solder fountain(s) typically use a miniature pumped solder wave with a spherical shape similar to the end of a pencil or Crayola to sequentially solder the PCB. This process is somewhat slower than the two previous methods, but much more accurate. The PCB may be fixed and the wave/wave solder pot moved underneath the PCB In 3-axis, or alternately the PCB may be articulated over a fixed wave/solder bath to perform the selective solder process. This process is generally regarded to be tool-less unlike to the first two examples.
- Laser Selective Soldering System are the newest systems and are able to import CAD-based board layouts and use that data to position a laser to directly solder any point on the board. The major benefits are thermal stress is eliminated, non-contact soldering process, consistent high quality solder joints, and maximum flexibility. Solder time can typically average 1 sec per solder joint. It may even be possible to eliminate stencils and solder masks from the circuit board to reduce manufacturing costs.
- Other less common selective solder processes include
- hot-iron solder with wire-solder feed
- induction solder with paste-solder, solder-laden pads, or pre-forms and, hot-gas including hydrogen with various methods of presenting the solder as above..
There are other selective solder applications that can be considered, some of which are non-electronic such as lead-frame attachment to ceramic substrates, coil-lead attachment, SMT attachment such as LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
s to PCBs, fire sprinklers where the fuse is low temperature solder alloys and many more.
Regardless of selective soldering equipment used, there are two types of selective flux applicators: a spray fluxer and/or a dropjet fluxer. The spray fluxer applies atomized flux to a specific area, while the dropjet fluxer is more precise, and the choice depends on the circumstances surrounding the soldering application.