Preliminary stage. Now, boards with no components assembled on the surface of board are called bare boards. More than four decades ago, soldermask didn't exist and copper lines were exposed to the air. Put in another way, this type of finished PCB is actually an exposed bare board. In this stage, components were assembled on PCB through lead plug-in soldering. Pad of PCB is a copper surface and solder wire with rosin core is applied to be soldered by soldering iron. Later, flux is coated on the whole PCB surface in order to protect circuit and solder pad and the coating method is mostly through flux of rosin and resin spraying. Of course, chemical silver plating is applied sometimes.
Primary stage. Since 1970s, PCB depended on flux to protect its circuit and passivation treatment was applied to stop copper oxidation by surface finish on pad, which aims to stop copper surface from oxidation. Solderability, however, was insured by second-time flux coating in the process of assembly. Then, some other types of surface finish came into being such as chemical gold plating, chemical tin plating, electroplated soldering and hot melting tin soldering and some products with high reliability applied electronickelling and electrogilding.
Maturity stage. At the beginning of 1980s, HASL started to be applied to take place of electroplated soldering and hot melting tin soldering. Meanwhile, OSP took place to substitute passivation treatment stopping copper surface oxidation and flux treatment with rosin coating. In the middle of 1990s, ENIG took off and ImAg and ImSn became mature as well.
Improvement stage. Advent of 21st century has witnessed new requirement on surface finish owing to the development of PCBs. In order to conform to RoHS regulations and implement lead-free PCB Assembly, electroplated tin lead alloy has to be totally eliminated and HASL containing lead has been reduced increasingly, replaced by lead-free HASL or other types of surface finish. With the development of PCB towards high density and fine spacing, pad space has to be fine and surface finish be smooth so as to adjust micro mounting component soldering assembly and chip metal line assembly so that application of lead-free HASL is being reduced. Performance of existing OSP and ENIG is improving as well and ENEPIG becomes pervasive. Requirement of high density and high frequency of PCB leads to advent of new nickel-free coating.
Up to now, diversity of application market of PCB leads to diversity of surface finish requirement and suitable surface finish and requirement should be selected based on different applications.
Boyunfa is a printed circuit board company, Located in Shenzhen,520 employees,16000 square feet, Who have offered PCB Manufacturing Service for more than 10 years.With the state-of-the-art technologies we employ, along with our highly trained workforce we are able to ensure that every PCB we provide matches your design requirements.