Selection and Testing of Electronic Components for LM

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Fig. 12 Computer-controlled test system for memory circuits, Macro-Data MD 104 M/MC Here equipped with a handler, which makes possible testing at Increased temperature Fig. 13 Test system Tektronix S-3260 Evaluation and checking of complex micro circuits both require such extensive measurements that special test systems are necessary. A minicomputer is used tor executing the test programs, which apply Incoming signals on certain of the component connections. At the same time measurements are made on the output connections. The test results are processed and are then shown on a display or as a printout Capacitors (excl. electrolytic capacitors) The capacitance value is measured with a comparison bridge, where the value is set up and the deviation is read off in percentage units. The dissipation factor is measured with a distortion factor meter. Voltage tests are carried out using a special voltage tester, which is set up for a certain voltage and which records the insulation resistance and any breakdowns. Electrolytic capacitors Capacitance, dissipation factor and leakage current are tested with a comparison bridge, where the capacitance and dissipation factor values are balanced out, after which the leakage current is read off on a special scale. Diodes and transistors The electrical parameters of these are measured using a go-no go tester with automatic input. SMall consignments are checked using a curve tracer. Micro circuits Micro circuits are subjected to rigorous checks comprising mechanical, environmental and electrical tests. The testing procedure is shown in fig. 11. The electrical testing of micro circuits deserves to be described more in detail. From the point of view of testing, the micro circuits can be divided into four groups, namely analogue, simple digital, complex digital and memory circuits, which require different types of advanced test equipment. Analogue circuits The parameters concerned are checked manually in test equipment type General Radio 1730. Simple digital circuits These are tested statically in test equipments type Teradyne J133 and Fairchild Q 901 "Qualifier".
Fig. 14 Diagram of the fault ratios for micro circuits distributed on a manufacturer basis Leakage faults check position 1 Electrical faults Leakage faults Electrical faults Cneck ,,,„„ 2 Leakage faults Electrical faults check pos|tlon , + 2 Different manufacturers Fig. 15, right Fault ratios for passive components and discrete semiconductors, obtained from computer system "Makon" Mechanical faults Electrical faults Complex digital circuits The circuits are tested from a functional point of view and also statically and dynamically. For this purpose the production side uses system Tektronix S-3260, which is shown in fig. 13. Memory circuits These are also tested as regards function and statically and dynamically. The test equipment used is Macro-Data M104 M/MC, shown in fig. 12. THE RESULTS OF INSPECTION ON ARRIVAL Inspection reports are kept for each individual inspection occasion. The reports are compiled once a month and the statistical data are processed with the aid of the LM Ericsson computer system MAKON (Material Control Purchase). Some results are shown in the histogram for micro circuits, fig. 14. The histogram contains statistics from two different inspection positions, where the inspection differs as regards the hermeticity test. In one place the trace gas used is krypton 85 and in the other helium. Fig. 15 shows the fault ratios for passive components and discrete semiconductor components. 103 FAULT TRACING COSTS-A COMPARISON Fig. 16 shows a comparison of fault tracing costs at different check levels. The figures are based on experience of actual costs. The diagram shows that it can be profitable to invest in more effective fault elimination methods in the inspection on arrival, forexample burn-in, in order to eliminate defective components that whould otherwise cause operational disturbances in the systems. FUTURE PROSPECTS Development of an effective and cheap method that makes possible a one hundred per cent check for gross leakages is desirable. Fine leakages in the encapsulation are then checked by means of sampling. Heat storage of components is replaced by burn-in with voltage applied and increased temperature. The increase in the complexity and speed of micro circuits requires large investments in systems for testing the functions and the DC and AC parameters during the inspection on arrival. The test system is equipped with a main computer that controls several check stations. The check stations for the inspection on arrival can work as independent units and utilize centrally prepared programs. Electrical function testing will to an increasing extent be carried out at an elevated temperature.
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