In electronic products, with the rapid increase in the use of small, light, thin and high-performance components, the position of assembly technology is becoming more and more important, and the relationship between assembly materials and environmental protection is becoming increasingly close.
Countermeasures against lead free welding include the following two aspects:
1, the development of alternative solder, lead-free soldering;
2, a new assembly technology to replace solder, namely lead-free solder process and equipment development.
All this means re evaluating existing connection technologies and developing new connection technologies.
Lead free soldering is on the agenda
In addition to the pollution caused by cleaning agents, electronic assemblies also contain heavy metals such as lead, copper, tin and other heavy metals. As is known to all, Sn-Pb has good weldability and quality assurance. It is easy to meet the requirements of electrical and mechanical maintenance and reliability of components. The process of reflow from jet welding to reflow soldering is simpler. But since tin and lead are both heavy metals, there is an urgent need for a reappraisal of this welding. In Europe and the United States, a tax related to the restriction and use of Pb for electronic welding has been initiated.
It is desirable to develop new lead-free soldering technologies that incorporate existing equipment and processes. Its specific requirement is that:
1) material cost is low;
2) has a melting point similar to that of Sn-Pb eutectic;
3) excellent electrical, mechanical and chemical properties;
4) compatible with existing process and equipment;
5) suitable for current assembly welding;
6) applicable to fine graphics. Unfortunately, no lead free alternatives have yet been found to meet the above requirements.
Development of solder bonding technology
Because of the miniaturization and narrow spacing of components, the limit of melting and welding has been put forward. In order to protect human living environment, lead-free soldering is very urgent. With the development of these factors, the development of solder bonding technology has been put on the agenda.
In fact, wire bonding of IC chip is a solderless connection technology, such as ultrasonic bonding (using plastic capillary and ultrasonic vibration, aluminum aluminum wire bond pads will be pressed on the chip and the shell) and hot welding (by high temperature melting and welding method, welding wire disc pressure wire bonding on chip and shell on the other). Originally, they are limited to special assembly parts, but has now developed to connect the IC to the board on the surface of various ultra electrode connection method.
The conductive adhesive (Ag, Cu) IC chip can be plated with gold solder or solder ball is directly connected to the substrate electrode, the insulating resin is filled between the element and the substrate, the expansion coefficient of the two different relaxation produced by thermal stress. Ensure assembly reliability. This technology has been used in the assembly of IC chips for LCD and mobile phones. It is reported recently that fine pitch connections smaller than 50mm have also been practical. The future subject of these methods is to reduce the contact resistance by expanding the applicable range of assembly. Before the severe challenge of environmental protection to the electronic assembly industry, the flux free connection is becoming more and more important because of the lack of cleaning and the simplification of the process.