In order to meet the requirements of SMA high quality and high reliability in the circuit board, FASTPCBA technicians share with you the main requirements for the assembly craft materials in the SMT craft?
(1) Good stability and reliability of solder paste. The solder is required to strictly control the content of harmful impurities; the solder paste and the flux are required to have low residue and no corrosiveness; the bonding strength is required to be not low or not high, so as to ensure that the solder can not be dropped during the welding process, It is convenient to take off the film during maintenance.
(2)Equipment that can meet the needs of high-speed production. The SMT production process is generally a high-speed automated process, and the craft materials should be adapted to it. For example, the curing time of bonding is about 20 minutes when the oven intermittent curing method is used in the middle and late 1980s, and the continuous curing method of the tunnel furnace commonly used in the 1990s requires the curing time to be within 5 minutes. It has a shorter curing time than the original.
(3) It can meet the needs of fine lead pitch and high density assembly. Fine lead pitch and high density assembly require finer grain size of the alloy solder powder in the solder paste; require solder paste and binder thixotropy better, less collapse;It is required to strictly control the solid content and activity of flux, so as to avoid bad phenomena such as bridging connection.
4) Can meet the ROSH environmental requirements. Many materials in traditional SMT craft materials contain substances harmful to the ozone layer and the human body, such as cleaning agents containing chlorofluorocarbons (CFCs) and lead-containing solders. With the increasing awareness of environmental protection and the increasing attention to human health, the research of harmless SMT craft materials is being strengthened.
The current solder is divided into lead-free and lead according to the amount of lead, and lead solder has been gradually replaced by lead-free solder. The characteristic of lead-free solder is that it reduces the harm of lead to people's living environment, has the advantages of high melting point, excellent tensile strength and strong fatigue resistance, and has higher requirements on the thermal stability of the flux and the welding craft and equipment.