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Printed Circuit Board Terminology
Published in Robert P. Hedden, Cost Engineering in Printed Circuit Board Manufacturing, 2020
Bare board testing is for shorts and opens. A short is electrical continuity where it is not desired, often caused by excessive copper between two circuit lines after etching. An open is a break in a circuit line, thus preventing electrical continuity. Tests for shorts and opens are done on the individual layers of multilayer boards, before and after assembly of the board. Testers may be loaded manually, semiautomatically, and fully automatically. Programs must be written for each part number. Some testers program themselves by checking a known good board (Marks, 1983). Typically, testing is done with a "bed-of-nails" test fixture. The nails are probes, usually on 0.100-inch centers, which make contact electrically between the tester and the points of contact on the board being tested. The bed of nails may address up to 32,000 test points. Defective coordinates are generally provided on a computer printout.
Hybrid Microelectronics Technology
Published in Jerry C. Whitaker, Electronic Systems Maintenance Handbook, 2017
Testing of flip-chip devices is not as convenient compared to TAB devices, since the solder bumps are not as amenable to making ohmic contact as the TAB leads. Testing is generally accomplished by lining the devices over a bed of nails, which is interfaced to a testing system. At high speeds, this does not realistically model the configuration that the device actually sees on a substrate, and erroneous data may result.
Design of three-section microneedle towards low insertion force and high drug delivery amount using the finite element method
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Liqiang Zhang, Chenxi Zhu, Jiakang Shi, Zhuoran Zhou, Daohan Ge
Needle 1 and needle 18 exhibit almost identical MIF, penetration efficiency, DDA and critical buckling force. But the SF of needle 1 is 1.86, which is much larger than 1.14 of needle 18. This phenomenon indicate that the MN base in needle 1 does not affect the penetration process of MN and provides additional strength under transverse load. Therefore, the rational base is vital for the design of MNs. Needle 19 exhibits approximately twice the MIF and DDA relative to needle 1, so they have similar DDA per unit load. It seems that they can provide about the same DDA in practical application. However, needle 19 has the lowest EPL of 75% among the five MNs. It should be noted that the fundamental deficiency of this explicit kinetic model in this research is that it only simulates the process of a single MN penetrating into the skin. In practical applications, the MNs mostly penetrate into skin in the form of an array, which may produce a ‘bed of nails’ effect if the density of MNs is relatively high (Olatunji et al. 2013). The larger skin local deformation around the needle 19 indicated by the low EPL may be exacerbated if needle 19 is made into an array, which will result in a lower EPL of middle needles in the whole MN array and then low DDA in practical applications. Besides, the large insertion force of needle 19 also causes some negative effects. Therefore, the TSMNs with appropriate size design are superior to the two-section MNs.