AbstractThe incentive to employ surface mounted devices (SMDs) in place of leaded components in high volume assemblies can be attributed to their improved manufacturing and performance properties. They are particularly suited to automatic placement and have an inherently greater reliability. Their small size and short lead lengths make their use especially attractive in miniaturised radio frequency circuits. However, to fully exploit the advantages offered by the technology, new design procedures must be developed and evaluated.
A review of relevant radio frequency design techniques and an analysis of surface mounted production processes were performed. These were used to compile a set of design rules for developing a miniaturised cordless telephone (transmitting at 1.7 MHz and 47 MHz). Its overall specification and features were based on an existing product manufactured with leaded components. This provided a benchmark against which to improve on performance efficiency, production costs and manufacturing repeatability.
In order to prove the validity of the new design it was necessary to subject the product to various approvals tests. These were conducted within the project and the telephone gained full approval for operation and sale in the United Kingdom. Through the experience gained during the course of the project an update to the initial set of design rules was made.
From the study it was concluded that, the higher self resonant frequency of SMDs over leaded components offers significant decoupling advantages in medium frequency circuits. SMDs also offer improved in-circuit tolerance because of the removal of insertion accuracy uncertainty. The use of SMDs at cordless telephone frequencies did not compel a change to the circuit design but further study is necessary to access the situation at ultra high frequencies. Singlesided, mixed technology was identified as an ideal surface mount assembly (SMA) entry technique because it maintains the familiar wave soldering process. In addition, it allows the optimum choice between SMD and leaded components to be made, in order to take advantage of cost/performance trade-offs and minimise acquisition difficulties.
|Date of Award||Oct 1991|