Keep it clean! Environmental chamber cleanliness has a direct impact on product performance.Sometimes the reason for cleanliness-related reliability concern comes not from assembly process and handling but instead from actual quality and reliability testing. Environmental chamber cleanliness has created substantial problems for several of our customers. Waters and cleaners used in environmental chambers can possess ionic i·on·ic adj. Of, containing, or involving an ion or ions. ionic pertaining to an ion or ions. ionic medication iontophoresis. residues that condense con·dense v. con·densed, con·dens·ing, con·dens·es v.tr. 1. To reduce the volume or compass of. 2. To make more concise; abridge or shorten. 3. Physics a. and deposit on boards. It is important to monitor these chambers for cleanliness to prevent harmful contaminants from being introduced onto finished assemblies and causing field failures. [TEXT NOT REPRODUCIBLE IN ASCII ASCII or American Standard Code for Information Interchange, a set of codes used to represent letters, numbers, a few symbols, and control characters. Originally designed for teletype operations, it has found wide application in computers. ] Recently, we have been involved in process monitoring and failure analysis for a manufacturer of high density assemblies. The manufacturer was seeing dendrites and a visible white residue that appeared in a drip pattern around a VHDM VHDM Very High Density Metric connector. The boards were double-sided no-clean assemblies using SMT (1) (Surface Mount Technology) See surface mount. (2) (Station ManagemenT) An FDDI network management protocol that provides direct management. Only one node requires the software. SMT - Station Management and through-hole on FR-4 laminate laminate, n a thin slice of porcelain or plastic fabricated in a dental lab, which is cemented to the front of the teeth to cover gaps, whiten stained teeth, or reshape chipped or broken teeth. . FTIR FTIR Fourier Transform Infrared (spectroscopy) FTIR Frustrated Total Internal Reflection FTIR Fourier Transfer Ir analysis showed only flux residues. SEM/EDX SEM/EDX Scanning Electron Microscope/Energy Dispersive Using X-Ray (Analysis) showed a concentration of tin, lead, oxygen and copper, indicative of electromigration-related failures. Using ion chromatography Ion-exchange chromatography (or ion chromatography) is a process that allows the separation of ions and polar molecules based on the charge properties of the molecules. we analyzed the localized connector and housing areas where white residue and dendrites appeared. Our findings showed high levels of chloride and sulfate sulfate, chemical compound containing the sulfate (SO4) radical. Sulfates are salts or esters of sulfuric acid, H2SO4, formed by replacing one or both of the hydrogens with a metal (e.g., sodium) or a radical (e.g., ammonium or ethyl). residues, which are often found together in tap water, but we had yet to diagnose the root cause of the failures. After examining the steps in the assembler's process, we analyzed the cleanliness of an ESS (1) (Electronic Switching System) A large-scale computer from Lucent used to route telephone calls in a telephone company office. The 5ESS is a Class 5 central office switch, and the 4ESS is a Class 4 tandem office switch. chamber used after assembly in a Malaysian plant. We analyzed the cleanliness of the filter and desiccant desiccant /des·ic·cant/ (des´i-kant) 1. promoting dryness. 2. an agent that promotes dryness. des·ic·cant n. , both used and unused. We also took wiping samples and foil samples from inside the chamber. All samples were analyzed using ion chromatography per IPC-TM-650, 2.3.28. Variability was plentiful among the foil and wiping samples, but many of the samples showed high levels of chloride residues (Table 1). Examination of the filter and desiccant showed very high levels of chloride residues, while unused samples and foil blanks showed low levels of residues. [ILLUSTRATION OMITTED] Our findings indicated that chloride residues were being deposited on the boards during ESS/burn-in testing. Contaminated contaminated, v 1. made radioactive by the addition of small quantities of radioactive material. 2. made contaminated by adding infective or radiographic materials. 3. an infective surface or object. tap water was permitted to condense and drip onto the sensitive VHDM connector, causing electromigration to propagate prop·a·gate v. 1. To cause an organism to multiply or breed. 2. To breed offspring. 3. To transmit characteristics from one generation to another. 4. and triggering field reliability concerns. To prevent the introduction of this contamination, we set up a cleaning protocol for the ESS chamber using Scotch Brite pads and 10 M[OMEGA] deionized water Deionized water (DI water or de-ionized water; also spelled deionised water, see spelling differences) is water that lacks ions, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. working from the top to the bottom of the chamber. The chamber should be scrubbed at least three times using this method, then thoroughly wiped with a lint-free cloth and DI water, making sure to clean all vents and air inlet openings. Then, the chamber should be wiped three times with isopropyl alcohol isopropyl alcohol: see isopropanol. using non-polyester critical contact wipes. The filter and desiccant need to be replaced, and clean DI water used when testing in the chamber is resumed. This case is one of several we have encountered that exemplify how critical chamber cleanliness can be to long-term field performance. We developed a cleaning program and rescue cleaned these no-clean assemblies for this manufacturer, but these frustrating problems could have been prevented by ensuring that chamber equipment and disposables were free of harmful ionic contaminants.
Table 1: Ion Chromatography Data
Ion Chromatography
Sample Description C[l.sup.-] N[O.sub.3.sup.-] S[O.sub.4.sup.2-]
Wiping Samples from Inside the Chamber
Left Side Wiping 7.44 1.76 1.62
Sample
Window Wiping 8.32 1.59 1.03
Sample
Back Wiping Sample 0.11 1.00 0.24
Back Wiping Sample 0.27 0.36 0.33
Back Wiping Sample 0.08 0.48 0.22
Back Wiping Sample 0.32 0.54 0.26
Top Wiping Sample 8.41 1.64 1.20
Window Wiping 5.76 1.99 1.22
Sample
Top Wiping Sample 11.76 1.06 1.49
Right Side Wiping 7.46 1.58 1.47
Sample
Top Wiping Sample 7.39 1.25 1.33
Left Side Wiping 8.19 1.36 1.14
Sample
Right Side Wiping 5.62 1.92 1.71
Sample
Right Side Wiping 6.97 1.88 1.48
Sample
Control Wiping 0.02 0.22 0.15
Sample
Left Side Wiping 5.52 0.97 1.71
Sample
Window Wiping 8.26 0.94 1.32
Sample
Foil Samples from Inside the Chamber
Foil 1 2.36 0.04 0.02
Foil 2 2.54 0.02 0.15
Foil-3 0.21 0.05 0.23
Foil 4 0.29 0.17 0.44
Foil Control 0.04 0.05 0.00
Standard Extraction of materials
Filter 206.73 24.45 1024.15
Dessicant - old 54.69 21.23 127.84
Dessicant - new 2.19 0.39 33.53
Ion Chromatography
Sample Description Na N[H.sub.4]
Wiping Samples from Inside the Chamber
Left Side Wiping 1.30 0.36
Sample
Window Wiping 1.77 0.61
Sample
Back Wiping Sample 0.24 0.27
Back Wiping Sample 0.41 0.22
Back Wiping Sample 0.23 0.26
Back Wiping Sample 0.69 0.27
Top Wiping Sample 1.21 0.61
Window Wiping 1.33 0.36
Sample
Top Wiping Sample 1.29 0.69
Right Side Wiping 1.24 0.65
Sample
Top Wiping Sample 1.27 0.98
Left Side Wiping 1.72 0.68
Sample
Right Side Wiping 1.28 0.54
Sample
Right Side Wiping 1.35 0.36
Sample
Control Wiping 0.17 0.05
Sample
Left Side Wiping 1.10 0.74
Sample
Window Wiping 1.43 0.26
Sample
Foil Samples from Inside the Chamber
Foil 1 0.18 0.06
Foil 2 0.24 0.23
Foil-3 0.39 0.36
Foil 4 0.29 0.29
Foil Control 0.12 0.01
Standard Extraction of materials
Filter 4011.34 1762.06
Dessicant - old 16.37 9.87
Dessicant - new 12.98 9.20
Terry Munson is with Foresite Inc. (residues.com); tm_foresite@residues.com. His column appears monthly. |
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