Issue link: https://iconnect007.uberflip.com/i/1527613
62 DESIGN007 MAGAZINE I OCTOBER 2024 For adhesive-based materials, we manufacture proprietary adhesives that are used to laminate a variety of films and copper foils to produce copper-clad base materials for circuitry manu- facturing. For adhesiveless materials, vacuum metalli- zation plus subsequent in-house copper plat- ing is used to produce Novaclad, the metal- lization technology used to produce the heat shield materials for the James Webb Telescope. In addition to materials and physical dimen- sion requirements, the customer presented an unusual electrical requirement, a resistance specification for certain nets. Electrical test- ing is a usual request from customers, so it is not unusual for us to design and build fixtures and program machines to enable this testing. However, this application required additional handling of technical aspects of testing and deserves the first detailed discussion. e customer's tolerances for net resistance were unusually narrow in range and required optimization of two different processes to meet the customer's requirements and still achieve a profitable yield. Because the cir- cuit was in prototype development at first, acceptable circuits could be quickly produced but at the cost of time-intensive manual test- ing and scrap from sorting good circuits. For viable production, however, a better test method, as well as optimized processing, was needed. e initial electrical test method had two main problems to overcome to provide proto- types for the customer in a timely manner: 1. Insufficient testing accuracy 2. Extensive testing time due to awkward manipulation of singulated circuits to test on opposite ends and opposite sides To solve testing accuracy, 4-point/wire testing was incorporated, involving Kelvin "probes" in the form of alligator clips with test probes, all gold-plated. Kelvin probes offer the advantage of eliminating the significant resis- tance of test leads from the measurement, thereby optimizing test accuracy, which is important for low resistance testing. e other testing problem was electrical test time, which was greatly reduced by taking advantage of the bussing for the final surface finish, rather than eliminating it by singulat- ing circuits with rule-die or laser, which breaks the bussing. e offal of each side is intercon- nected during the copper plating used to plate the vias. e interconnection of the offal, which includes the bussing, allows testing with probes near each other to test a net with test points far away and on opposite sides of the circuit. A precise correlation of test results was sta- tistically determined between bussed circuits, bussed circuits with final surface finish, and singulated circuits with final surface finish. is correlation enabled testing sooner dur- ing production whenever needed and espe- Figure 1: Novaclad Diclad roll form. Figure 2: Sheldahl Novaclad flexible circuit processing.