SMT007 Magazine

SMT-July2016

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18 SMT Magazine • July 2016 004B IPC TM-650 2.6.3.7 surface insulation re- sistance test and IPC TM-650 2.3.25 in an at- tempt to investigate the correlation of ROSE methods as predictors of electronic assembly electrical reliability. Introduction Ionic contamination testing has been traced back to work done at the United States Naval Avionics Center in Indianapolis in the early 1970s by Hobson and DeNoon 3 . This work eventually led to the development of the 1.56 µg/cm 2 (10 µg/inch²) NaCl equivalent standard for ionics extracted using an IPA/water mixture. High volume circuit assembly at the time used only wave soldering processes, employing foam fluxers to apply RMA flux followed by a post soldering cleaning process with fluorocarbon solvents. This ionic contamination limit became part of now defunct Mil Spec P-28809 4 and Mil STD- 2000A, but has been carried through versions A through F of ANSI/J-STD-001. This manual pro- cedure has become more automated with the invention of descriptively branded test equip- ment such as the Contaminometer, Ionograph and Omega Meter. Although these measuring devices improve the efficiency and accuracy of measuring ionic contamination soluble in alcohol/water mixtures, they also increase the amount of ionic material measured 5, 6 . IPC-9202 describes a procedure for qualify- ing a process for electrical reliability by measur- ing SIR using IPC TM-650 2.6.3.7 and IPC TM- 650 2.3.28 by using the IPC-B-52 test coupon. This coupon is shown in Figure 1. The standard calls for a minimum SIR value of 100MΩ, but only calls for a measure and report of the ionic contamination. The reported ionic contami- nation then becomes a benchmark for "future trouble shooting or process improvement ef- forts." The experiments carried out in this work were designed to use methodology derived from IPC-9202 to determine if it is possible to have a solder paste that passes SIR standard of >100 MΩ, but fails the ionic contamination level of ANSI/J-STD-001f, and determine if a second sol- der paste fail the SIR test and pass the ROSE test standard. DIVERGENCE IN TEST RESULTS USING IPC STANDARD SIR AND IONIC CONTAMINATION MEASUREMENTS Figure 1: IPC B-52 test coupon comprising a SIR test coupon (SIR) and a section for ionic contamina- tion measurements (SIR). Component ID: 1 – TH connector 4 x 24 pins; 2 – Capacitor, 10 pF, 0402 package; 3 – BGA, 256 IO, 1 mm pitch, isolated; 4 – SM connector IEEE 1386, 2 x 16 pins; 5 – Capaci- tor, 10 pF, 0805 package; 6 – QFP160, 0.65 mm pitch, isolated; 7 – QFP80, 0.5 mm pitch, isolated; 8 – Capacitor, 10 pF, 0603 package; 9 – SOIC16, 1.27 mm pitch, isolated; 10 – Capacitor, 10 pF, 1206 package.

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