The invention relates to a lead-free soft solder, especially for use in electronic and electrical engineering. A diaphragm is located roughly in an opening of the enclosure surrounding the gas cavity and attached to the enclosure by an outer suspension member. ; and two of R40, R41 and R42 are C1-6 alkoxy while the remaining one is methoxymethyl, etc. The longitudinal direction becomes substantially parallel to a direction joining the micro-structure for light-scattering with the point light source. Moreover, the needle seats can be replaced by needle rollers.