Lead-free SMT process and accelerate the conversion of the problem for pcb assembly services
Design issues
A smooth transition to lead-free manufacturing will take some time, industry began to design the best lead-free products now. New product testing, identification, and many supply chain issues, the industry involves many departments, design is complete, these issues need to take up a lot of time.
The definition of lead-free
So far, the definition of lead-free packages have not yet been formally identified. BGA solder balls for wire coating and the European Union under the lead-free threshold Pb <1000ppm; JEIDA also as Pb <1000ppm. JEDEC was originally recommended pb <2000ppm, but recently decided not to lead JEDEC set a ppm value. As the sub-contract manufacturers and EMS office around the world, lead-free definition of uncertainty, making the SMT materials and the selection and appraisal process is more complex. The official launch of the EU rules, the definition of global standards with a lead-free as possible.
Quality and reliability standards
Existing standards for the IPC process leaded product. SnPb alloy has been used now for decades, IPC standard for the product definition of the minimum acceptance criteria, customers and suppliers to use this standard for the reception and rejection decisions. Lead-free alloys, in order to avoid errors in interpretation of the product acceptance criteria need to establish a new standard. Lead-free solder joints after reflow visual appearance of the problem is a description of this problem can be a good example. For example, pure tin solder joints more than SnBi light, which is not trained inspectors have doubts. In addition, to be established quality standards, should also be easy to SMT production line operators and inspectors training. Lack of available technology to determine the issue of standards may lead to costly delayed delivery occurred.
Tin whisker (whisker) caused great concern because it is very obvious. Although there are many independent studies have been reported, the industry is still no standard procedure for tin whisker testing. Recent IPC / JEDEC lead-free, held in Taiwan on the international conference, there are several companies using different test methods published on tin whisker growth study report. Experimental results show that standardization is important for lead-free solder solderability testing and reliability testing have to be standardized. If the world to receive the test method, the identification of lead-free components, the time will be shortened, repeat testing can be reduced, thereby reducing the cost of customers and suppliers. Figure One Toshiba pre-coated on both SnPb and Pd Pd PPF (pre-plating-frame) of the specimen wetting and solder joint tensile test results, you can see, SnPb and SnAgCu solder SnAg coating of lead painted and Pd PPF wetting layer, and the solder wetting of SnPb coating is similar.
Toshiba also welded components on the PCB solder joint tensile strength test done. Experimental results show that these lead-free coated wire tensile strength and tensile strength of conventional SnPb-coated wire on the same level. SnAg solder and Pd PPF strength test, showing that they are satisfied with the reliability of strength.
Backward compatibility and forward compatibility
The transition to lead-free pcb manufacturing can not be completed overnight, SMT assembly line may use dual-mode manufacturing line, that is also used in the production of leaded and lead-free materials for assembly. This includes the use of lead in lead-free processing components - has lead components can be used as lead-free process forward compatibility (forward compatible), or in a lead-free components used in the pcb assembly process - this is called after the compatibility (backward compatible). This also has the best two-way compatibility, however, still need to overcome many technical difficulties. Most lead-containing products are controlled at maximum reflow temperature 240 ℃, and according to JEDEC J-STD-020B, lead-free solder reflow peak of 240 ℃ -250 ℃. Semiconductor suppliers must be based on J-STD-020B re-define its sensitivity to wet component (MSL). The new standard set of peak temperature for large packages (> 350 mm3) 240 ℃, and small package 250 ℃. Figure 4 is a Toshiba recommended for leaded and lead-free temperature curve.