This invention concerns a method for manufacturing and making planar contact with an electronic apparatus, in particular a high frequency module.
Mass production of radar modules on the basis of bare chip processing, in particular for an operating frequency of 77 GHz, traditionally uses so-called wire bonding methods. Operating frequencies in the 77 GHz range are used, in particular, for so-called long range radar, e.g. as the basis for longitudinal vehicle control. Traditional wire bonding provides only slight process reliability of the chip contacting technology which is used. Traditional wire bonding has a big effect on costs. In the wire bonding process, which disadvantageously is serial, wire bonds, with lengths e.g. from 0.3 mm to 0.4 mm, are to be produced with a precision of, for example, about ±5%. Because of the numerous contacting points in a traditional radar module, the unit costs are very high. Despite some system advantages, therefore, the so-called 77 or 79 GHz radar technology has disadvantages compared with competing technologies such as LIDAR (which is based on scanning the environment by a radar beam). The costs of production (assembly) cause the greater part of the system costs. In particular for Europe, a change from 24 GHz technology to 79 GHz technology seems necessary. There is therefore a need for inexpensive packaging solutions. Monolithic systems, in which the whole radar front end is combined on one chip, also seem not to be available in the near future. Use of the so-called flip-chip technology seems disadvantageous because of the stimulation of oscillation modes between chip and substrate and bad heat spreading. Use of the surface mount technology (SMT) which is traditional for 24 GHz radar modules is also disadvantageous, because of the high frequencies which are used. According to the related art, thinned HF (high frequency) chips are glued very precisely to a substrate board using an electrically conducting adhesive. For this purpose, from the insulating film which covers the whole surface of the board, an opening or window for the chip is cut by laser. This window is slightly larger than the chip, resulting in a narrow surrounding gap. The surrounding air gap ensures potential isolation between the upper and lower sides of the chip (earth), without parasitic capacitances. The chip and insulating film have approximately the same thickness. All HF (and LF) signal lines are on the insulating film, and so are all supply lines. According to the traditionally used wire bonding process, the chip pad and HF line are connected to each other. In some circumstances, direct chip-to-chip connections can also be implemented.
According to the related art, an insulating film is put onto a substrate board. At least one window for at least one chip is lasered into the insulating film. A thinned HF chip is glued onto the substrate board in the window using an adhesive. According to the traditional method, contacting areas of the chip and electrical lines on the insulating film are contacted by wire bonding. Traditional wire bonding must be carried out serially, and therefore has a big effect on costs and is very slow.