Microcorrosion Analysis and Their Effect in the Operation of Industrial Equipment of the Electronics Industry of Mexicali

of the electronics industry, as based on the presence of atmospheric and climatic parameters. The analysis was made with the specifications of ASTM standards, and was determined the CL. This analysis simulates the deterioration of electrical

of the industrial equipments and machinery with MED. Corrosion in microelectronic devices is known as microcorrosion and is not detected at naked eye in the manufacturing processes, until the MED fails and causes uncontrolled situations in industrial plants, and preoccupy to specialized personnel, managers and owners. The microcorrosion is observed only by the SEM technique and other micro and nano procedures (Gustavo López B. et al, 2013). The indoor pollution generated by variations of climatic factors and CL of chemical agents from the outdoor sources, originated aggressive environments and the deterioration of materials very fast. For this reason, the MED are manufactured according to their functionality and corrosion resistance. At present, the materials used in the electronics industry in the world, are: aluminum, copper, chromium, tin, nickel, gold, palladium, platinum, silver, titanium, tungsten and copper alloys, tin-silver-palladium (Bella, 2002).

Electronics industry
The electronics industry has grown tremendously, and have a lot relation with other industries, increasing gradually in the developing countries, with a wide variety of electronics manufacturing equipments, which are used frequently (

Design of electronic equipment
Sometimes, microelectronic devices with metallic materials from suppliers are affected by corrosion in the transportation process, in the reception of materials and in the storage of these MED (Lopez Badilla G. et al, 2011). Personal of warehouse of the electronics industry report some MED deteriorated each week of the year in this region of Mexico. Sometimes are reported the cases when it fails in the manufacturing processes or with the users, and is necessary pay the warranty generating economic losses (G. . Factors as concentration levels of sulfurs mainly formed by the presence of hydrogen sulfide (H2S) and sulfurs oxide (SOX) that exceed the AQS principally in the winter season, and the variations of RH and temperature, promotes the formation of aggressive environments in indoors of the electronics industry and originates very fast the corrosive phenomena in this city, that deteriorate the MED very fast (G. L. . Corrosion in metallic materials used in the electronics industry are similar for other materials, but with two differences: being the first the applied voltage (105 to 106 V / cm), causing deterioration in the majority of MED by the uncontrolled flow current between conductors and ionic impurities (ASHRAE, 1999). The second difference is the size of components that are sometimes microns and require very low concentrations of pollution and film moisture to generate corrosion (Tahara A. et al, 2005). This cause electrical failures of any microelectronic device in short periods. Some electrical failures in these types of components have been reported by the migration of ions released during the formation of corrosive agents as metal oxidation, reducing to the cathodic process and generating dendrites (Lopez Badilla G. et al, 2013). This originates conductivity between the electrodes, allowing the growth of whiskers (being a detachment of metals) principally in cadmium, tin, gold, silver, zinc and copper-nickel alloy. Corrosion in welds is also considered important because it causes lack of adequate adhesion of the MED in the electronic boards (Gustavo ).

Industrial operations in the electronics industry
Technological advances in the electronics industry require increasingly smaller devices as the MED, with more components in their encapsulated and with major quantity of functions (Lopez Badilla G., 2008). The Micro Metal Oxide Semiconductor Field Effect Transistor (MMOSFET) and the Micro Bipolar Junction Transistor (MBJT), which are the most important basic electronic components in the electronic devices and systems, are developed as a special semiconductor with smaller dimensions than 0.1 microns (G. . The number of functions of the MED depends on the amount of components increasing their operation capacity. The silicon semiconductor structure protects the internal elements of variations of RH and temperature, external connections to the chip and can dissipate the heat generated internally. A great advantage of use a material as copper in the MED is for their low cost and good electrical and thermic properties (G. López Badilla, et al, 2013), but is very susceptible to the corrosion phenomena. (Abdulaziz, 2003). The electronics industry which is located in the Mexicali city, have a wide variety of MED in the industrial equipments and machinery, and sometimes in indoors of these companies, are exposed to uncontrolled environments, generating the fast deterioration of electrical connections of the MED. In the manufacture of electronic devices and systems that is performed in the electronics industry, are presented four main steps, as mention in the figure 1. These stages are: (a) storage area, where are collected materials for the production process, (b) manufacturing zone, where is transformed the raw material, (c) inspection area where is evaluated the quality of products and (d) shipping zone where is installed the final product to send to customers Lopez B. G. et al, 2007).

Atmospheric corrosion in the electronics industry
Atmospheric corrosion is an electrochemical phenomenon generated by a wet film formed on the metallic surfaces of metals as copper used in the MED, where sometimes is visible and in other is invisible (Gustavo L. . This film is the electrolyte where the metal is dissolved, generating the metal ions movement, which promotes the corrosion phenomenon. The corrosion products forms dendrites and whiskers on the connections and joints of microelectronic equipment connectors. A feature of the electronic components is its design that avoids the accumulation of water, by variations of moisture. These are important factors in the formation of the electrolyte layer which cover the metal (Cerrud-Sánchez. S.M et al, 2005). The film formed on the metal surface of metals used in the MED utilized in indoors of the electronics industry, is thinner than the film formed in metals exposed at outdoor conditions. It requires a very precise analysis to detect the electrochemical process, indicating that the corrosion in indoor environments is different type that in the outdoor zones. This mean that the analysts of corrosion, specialized methods to detect the corrosion phenomena in metallic materials used in microelectronic devices and systems, with greater capacity and at micro scale to detection the corrosion, to reduce and control this electrochemical process. Air pollutants with more aggressiveness are the H2S and SO2 emitted from the principal outdoor source near of the Mexicali city, called the Cerro Prieto geothermal field, located at 25 km of this city, and these chemical agents are emitted and dispersed to the Mexicali city.

Corrosion in the electronics industry of Mexicali
Presence of corrosion of metals used in indoors of the electronics industry in Mexicali appears as an electrochemical process involving two aspects: wet and dry climate combined with the presence of H2S and SOX mainly. This increases the corrosion rate (CR). In Certain pollutants in an area of the city and its valley, reach other zones and in some times with lower levels are generated the aggressive environments and the corrosion process. It is for this reason that this research was developed to evaluate the indoor atmospheric corrosion in a company and the correlation with the production yielding of the industrial equipment and machinery. Besides the air pollutants mentioned which influence the corrosion process, there are other small particles that cause the formation of corrosive agents as microorganisms (Leidecker, 2006). Analysts of microcorrosion, mention that the absorption method is the best technique to evaluate the corrosion products of copper, nickel and zinc. This indicates a strong influence of carboxylic acids and organic species, such as acetates, oxalates formats and internal emitted by anthropogenic sources as burning wood and tires, that are small aspects in the electrochemical phenomena, but generates deterioration in metallic surfaces of electronic devices (Fontana, 1986). An example of the formation of corrosive agents is shown by a study conducted in Japan with the comparison of metals of copper and tin, after three months of exposure to sulfate occurred in the electronic industry of Mexicali is showed next in Figure 2.

Comparative studies of microcorrosion
Several studies mention about the effect of microcorrosion generation in the operation yielding of microdevices used in the electronics industry. This process of analysis indicates that at the minimum presence of corrosion in these electronic components, generates a significant impact on the deterioration of electronic microdevices. Below, shows a descriptive analysis of some studies in various areas of the world in Table 1.

Methodology
Water exists in the atmosphere as liquid phase, steam and solid. Moisture levels depend on the steam pressure which exists in a particular environment. The RH and temperature were the most important climatic factors in this study, which promoted the increase very fast the CR. The information of air pollutants, temperature and RH by periods daily, weekly, monthly, seasonally and at the year, was obtained and organized by the EMS (Environmen

Statistical information
The pollutants H2S, SO2, NOX O3 and CO detected by the EMS in the outdoor environments Mexicali, which penetrate at indoors of the electronics industry. This mixture of air pollutants, together with variations in moisture and temperature, rises the CR of MED used in the electronic equipment. For the correlation analysis data were used periods where the RH and temperature were above 70% and 35 ° C, and the concentrations of air pollutants mentioned above that overpass the levels of AQS. The information obtained was organized in tables with the corrosion of metallic surfaces of the MED analyzed to determine the degree of correlation between climatic parameters, contamination and corrosion.

Environmental monitoring
The air pollutant data was obtained with specialized equipment containing data acquisition systems specialized and organized on a monthly, controlled by the EPA.

Scanning electron microscopy (SEM) technique
This technique was used to determine the chemical elements from compounds which react with the metallic surfaces of the MED analyzed. The electrons flowing through the low energy generated by the instrument topography showed electrical connections of the MED corroded, indicating the particle analysis, detection of defective MED and the metallurgical defects. With this technique, were determined the chemical composition observed in a spatial distribution of metallic surfaces of MED damaged. This was made in order to know which of the pollutants reacts in the metals to know the chemical agent with major influence in the generation of the corrosion process. A distinction was made between the different possible compounds for the oxidation state of the metal ions involved in the corrosion products. This allowed observe the morphology of corrosion products on the surface depending on the elemental composition. This technique is known in detail, quickly and accurately, to determine the structural form and location of corrosive agents, with which we determined the type of corrosion (uniform and pitting, which are the more common presented in the electronics industry of Mexicali), to suggest the best possible methods and techniques protection for metallic materials of the MED.

Results
The origin of corrosion in indoors of the electronics industry was due to variations of the climatic factors that were mentioned above and combined with the presence of sulfurs principally in the Mexicali city. In the winter season, appeared uniform corrosion by the wetting film formed on the metallic surfaces of the MED, and in the summer period, was generated the pitting corrosion in these materials by the occurrence of some droplets that adhere to certain areas of the metal surface. This is partly was due to the wetting time (also called time of wetness (TOW), which is an important factor of the origination of the corrosion phenomena). The TOW was obtained with the evaluation of RH and temperatures above 75% and 35 °C that is common in the city analyzed in the majorly of periods of the year.

Evaluation of climatic factors
In this study, the corrosion process initiated in indoor atmospheres of the electronics industry of Mexicali city, influenced by external climatic conditions (Gustavo L. . The wetting time obtained with the RH and temperature of the city of Mexicali, shows high rates in some winter and summer periods, being an important factor for the type of corrosion that occurs in metals used in the MED of industrial plants, and the levels at which the CR increases. In this process are formed some voltage electrodes, for example in the binding of copper to tin the voltage was 0.2 volts, and caused an electrical malfunction. The minimum wetting time in the winter period was presented in December with a value of 58 cycles and the maximum peak was in February with 163 cycles. This occurred with a temperature range in outdoor environments from 4 •C to 24 •C, resulting in a negative effect in the indoors environments of the electronics industry. In the summer period from July to August of 2012 the RH is greater than 75%, and temperatures above 35 •C, and some droplets were formed in some areas of the metal surface, generating selective corrosion of metal parts, being mainly pitting corrosion. In change, in the winter seasons from December of 2011 to January of 2012 with indices of RH and temperature higher than 90% and lower than 20 °C, occurred the formation of the wetting film in the entire metallic surface presenting the uniform corrosion. The wetting time in the summer period of 2011 was 47 cycles as the minimum level presented in June and the maximum was 135 cycles in August. This factor was very essential to know the kinetics of corrosion in MED, being with major effect in summer than in winter by the presence of pitting corrosion. The TOW influenced in the velocity of deterioration of MED presented a CR higher in the summer periods than in winter seasons due to the effect of temperature (greater than 35 •C) that is showed in figure 3. The design of electronic components and equipment, such as size, structure and characteristics of the metal surface is essential to prevent the corrosion phenomena. At the beginning of the analysis period was less the TOW, in the summer month with 0.22, but increases from 3AM and 9AM to its maximum value of 0.57 and started down to get close to 0 from 24:00 to 6PM. In February, there were initial values of 1:00 a.m. to 3:00 a.m. 0.25 and maximum of 0.38 at 5AM where it remained and began a descent from 8AM and stay between 0.1 and 0.2 and increases again from 8PM to a value close to 0.3. These cycles of wetting time indicated the duration of the corrosion process in metals generated electronic equipment and the formation of corrosive agents in connections and electrical connectors. The influence of cold air causes the temperature in a metal surface, decreased below the dew point, with the RH levels higher than 80% and was formed on the metal film. This occurred in Mexicali in the period of the study, causing corrosion, which depended on the size, orientation and surface characteristics where the phenomenon caused. With the ISO 9223 standard, levels were determined the wetting time, with the lowest effect T1 and T5 that a major factor in the deterioration of metals used in the electronics industry. In this city, even if the wetting time has levels from T1 to T3 (in annual period), and T1 and T2 in February, August and November, corrosion is generated by regional climatic variations. The annual analysis shows the hours where there were peaks of TH 5AM being at 7AM and in this period were additionally obtained the hourly averages, standard deviation and minimum, to know in more detail the process of film formation on surfaces metallic materials evaluated (Table 2).  This evaluation was performed for the periods in which need have better control of indoor climate controlled the industrial plants of this city.

Analysis of environmental pollution
Data of air pollutants obtained by the EMS showed interesting information to determine the principal chemical agent in the deterioration of the MED. In this section of the study, were evaluated only the pollutants with the different ranges of the NO2, O3 and SO2, and not analyzing the CO for their ranges greater than the by monthly periods. The analysis was made at the times of this chemical agents overpassed the AQS in daily periods representing in percentages days of the 2012 as showed in figure 4. Higher levels present the SO2, NO2 and follows after O3 in 2012 year where the values increased to almost 56 % of times overpassed the AQS for SO2, as the maximum level in January and December and the minimum indices was 8 in July. For NO2, the maximum index with 34 was in January and the minimum level was 4 in July. And to the O3, were 28 in January as the maximum level and 2 in July as the minimum index. The air pollution periods varies in different hourly, daily, weekly, monthly and yearly periods, after by the traffic vehicle and industrial plants mainly, which originates the formation of greenhouse effect principally in the winter season and the dispersion of pollutants in the Mexicali city depending the wind direction and speed. The indoor atmospheric corrosion of the electronics industry has been controlled but not eliminated in cleanrooms, and sometimes metals like copper have spots that indicate the onset of corrosion. The atmospheric corrosion in indoor environments is reduced when they controlled microclimates, which increases the performance of electronic equipment. The environments without climate control, the corrosion rate increases rapidly, damaging metallic materials. The deterioration of metals in February was lower than in August as temperatures above 35 •C. In winter SO2 concentrations have a large effect on the poor productive yielding of the MED and thus industrial systems and machinery. It was easily dispersed into the atmosphere and easily adheres to metals, but the corrosion process is slow. The correlation of SO2 at low levels of RH and temperature deteriorates the MED too, mainly in the months of February and August. An analysis of the CR according to the formation of corrosive agents in joints and connections was made, and were higher in August than in February, as a result of higher temperature ranges. In winter we evaluated the wet film formation and corrosive metals and concentration indices of air pollutants.

SEM evaluation
The SEM analysis shows the grade of deterioration in the MED electrical connections of the MED. The microphotographs were obtained of the microelectronic devices damaged. An evaluation indicates at least 10 electrical failures at week of the MED as was observed in figures 5 and 6. At macro levels are not observed the deterioration of the materials, but in the SEM analysis were showed the great effect of the corrosion process. To detect very fast the corrosion phenomena, was necessary considering always the use of microanalysis with the SEM technique. Figure 5 shows some MED damaged by corrosion at 500X and after was made an evaluation at 5X to detect with better precision the deterioration of the MED corroded in the spring and summer periods of 2012. At 5X, was observed the formation of the uniform corrosion in spring in the majorly if the metallic surfaces of electrical connectors and connections of the MED. This was promoted by variations of the RH principally. In change in the summer season indicates the presence of in a small section of the metallic surfaces the presence of uniform corrosion and tending to appear the pitting corrosion, being an important factor for it the high levels of temperature. In Figure 6, are showed the analysis of the autumn and winter periods, indicating in the autumn season, a great deterioration represented by the black sections, promoted by the levels higher than 80% of the RH. In the winter period, the appearance of uniform corrosion in the majorly of the metallic surfaces, indicated a similar deterioration as in the spring season by the variations of RH. This shows the kinetic of the corrosion process in different season of 2012 and the mechanisms that promote this electrochemical phenomenon. The importance of analyzes the phenomenon of corrosion in metallic materials used in the electronics industry in Mexicali, is to assess the negative effects of corrosivity levels in the indoors of the electronics industry in Mexicali city. The metals used in the MED electrical connections were constituted of copper, gold, silver and tin mainly.

Conclusions
The presence of corrosion in the MED caused the low productive yielding in industrial equipments and machinery. The mathematical correlation was made from the information obtained of the pollutants that was adhered to the metallic surfaces. The chemical agents were emitted from outdoor sources and penetrate to the indoor environments, through holes, cracks or air conditioning flow. The uncontrolled climate parameters as humidity and temperature, promoted the formation of a wet film on metal surfaces, generated by the corrosion process. The deterioration of materials generated bad function in the microelectronic devices due to inappropriate conductive paths (dendrites) formed between connections unnecessary electrical connections. The dendrites formation was due to migration of metal ions released by the etching process, which presents a voltage caused by corrosion current as a flow between conductors in the presence of mobile ionic impurities. Thus, electrical currents are generated in the order of micro amperes components alter their function by electrical failures and reducing its operational performance. Most components require specific values of current and voltage for operation, or they stop working. The corrosion phenomena observed in various metallic materials used in the electronics industry was similar in some phases, as was indicated by other studies. However the metals that constitute the MED showed different types of corrosion at the final stage depending on the environmental conditions. Corrosion was a problematic situation in the electronics industry of Mexicali, even in clean rooms. The develop tests to detect the origin and occurrence of corrosion is difficult for the complexity of the microelectronics devices, and lack of controlled indoor climates. Climatic factors, combined with the fine particles and gases such as hydrogen sulfide, sulfur dioxide, carbon monoxide and nitrogen oxides, which sometimes exceed the air quality standards in the region, generating harsh environments in indoor of the electronics industry, causing the corrosion phenomena. One of the principal emission sources which generate aggressive atmospheres in indoor of the electronics industry of this city was the geothermic plant that supplies electricity to Mexicali city and their valley and some cities of United States. Other minimum emission sources are the traffic vehicle, industrial plants, soil erosions and microorganisms. These pollutant particles adhere to the metal surfaces with or without the film formed by climatic variations and start the corrosion process. Also, with levels greater than 80% humidity and 25 •C that is common in the Mexicali city was obtained the TOW cycles, which indicates the periods in which a metal surface remains wet enough to give way to a process electrochemical corrosion to occur.