Issue link: https://iconnect007.uberflip.com/i/374650
20 The PCB Magazine • September 2014 the surface of the aluminum. In subsequent processing the aluminum component board is first coated with an insulating material and then circuits which interconnect the compo- nents are applied using buildup technologies. An example of a solderless test vehicle assembly is shown in Figure 1. The balance of this article will describe in more detail the processes used in the manufac- ture of such product and enumerate the numer- ous benefits that can be derived by simply re- versing the manufacturing process. That is plac- ing circuits on component boards rather than components on circuit boards. Basis Manufacturing Concept A new process for manufacturing a PCB which is comprised primarily of aluminum is hereafter described. The novel process bypasses completely the soldering process in accordance with the precepts consistent with what is known as the Occam process [1,2] . The Occam process is a subset of technologies that fall under the gen- eral umbrella term of SAFE an acronym which stands for either "solderless assembly for elec- tronics" or "solder alloy-free electronics." SAFE manufacturing is relatively simple compared to traditional circuits, and the cost should prove significantly lower. In brief, the process is carried out by plac- ing electrically tested and burned-in electronic components onto an aluminum carrier plate/ housing. This can be performed using tradi- tional pick and place equipment. The resulting structure is fundamentally a component board. Following secure placement of the components, processing methods traditionally used for the manufacture of HDI buildup boards are carried out on the surface of the component bearing aluminum assembly to produce circuit patterns with the interconnection between components and circuit pattern being effected by copper plating of both the circuit features and the vias which interconnect component leads to those circuit features at desired locations. One advan- tage of note at this point is that unlike soldered devices, only those component leads requiring connection need be provided with vias. In ad- dition, the vias are smaller than the traditional solder lands so more surface area is available for including cleaning of baked on fluxes follow- ing the high temperature assembly process. Lead-free solder also had spillover effects on the PCB laminate material itself as manufacturers experienced delamination and degradation of the resins used in traditional circuit construc- tion. One more recently encountered problem is a phenomenon referred to as pad cratering, wherein resin beneath the copper land to which a component is attached is actually torn loose from the surrounding resin breaking through the copper and causing an open. In this environment, an alternative ap- proach to manufacturing electronic assemblies has been conceived and is presently being de- veloped. The new method in simplest form is one which eschews the use of solder and is predicated on the use of aluminum substrates which house fully tested and burned in com- ponents to create what can be best described as a component board wherein the terminations of the components are proximately planar with ALuMINuM BASE CIRCuIT TECHNOLOGy continues figure 1: aluminum is a viable alternative to customarily used laminates when solder is not used to make interconnections between compo- nents and circuits. aluminum is unique in that its surface can be anodized, creating an insula- tion layer of alumina which can be colored and sealed. all components shown have a purposely selected 0.5mm contact pitch for reasons discussed in the text.