Stray current corrosion:
Stray current is the current which occurs when conductors are placed between high magnetic or electric fields. Presence of stray currents over the PCB surface can generate corrosion problems. The below figure 5 shows severe corrosion damage to micro wave module for 24 GHz. This equipment is built in controlled conditions where water condensation is possible. After few hours of use, severe corrosion was seen on the surface. Figure 5. Stray current corrosion of a micro wave module for 24 GHz used in a control equipment.
Behavior of an active-passive metal: Behavior of metals is divided into three zones. They are as following
1) Active
2) Passive
3) Transpassive
Metal or alloys which initially demonstrates behavior …show more content…
Among all the common metals we take nickel because it has many applications in electronic industry, for an example as a diffusion barrier on electrical contacts and as an electrical conductor on devices. Oxidation of nickel takes place at 100 degrees centigrade and is more sensitive to relative humidity (RH) than to the temperature. Film thickness increases with increase in RH and forms Ni(OH)2 at the surface of NiO film with creation of vacancies in the surface of the oxide. NiP alloys are used as a material for electrical contacts and for metal interconnects. A passivating film is formed at temperature up to 200 degrees centigrade and with thickness ranging from 0.6nm to 1.5nm. Based on study using Auger electron spectroscopy and X-ray photoelectric spectroscopy (XPS), it was found that the oxidation product is an layered structure, which at steady state consists of an inner layer of a nickel phosphate, a middle layer of NiO and an outer layer of Ni(OH)2. These layers are observed by AES depth profiles and by angle-resolved XPS (in the below figure 6). In this Figure 6, we see that at the low, more surface sensitive angle of of 18 degrees, the Ni(OH)2 peak is greatly enhanced and the Ni3(PO4) 2 peak is mostly suppressed compared to the peaks at a takeoff angle of 81 ° at which the signal comes from a greater depth. The peak at NiO is slightly suppressed at 18 degrees but not nearly as much as the phosphate …show more content…
When applied voltage is present even gold is subjected to electrolytic corrosion in micro electric circuits. Generally most of the IC’s applied voltage between conductors is 5-10 V. However, in the presence of sufficient adsorbed moisture on the dielectric, the fraction of the applied voltage that appears across the anode/substrate and cathode/substrate interfaces can be sufficient to sustain an electrochemical reaction. Frankenthal and his co-workers studied the behavior of gold in sulfate solutions containing various amounts of chloride. They found that active transition takes place in all solutions from 1M H2SO4 to saturated NaCl. Figure 7. Anodic polarization curves for Au in 1 M H2SO4 with HCl additions.
Failure mechanism of a discrete semiconductor device was caused by a resistive film of Cr2O3 that had developed between solder connections and metallization to other system components. Figure 8. Anodic polarization curves for Au in unstirred NaCl
Stray current is the current which occurs when conductors are placed between high magnetic or electric fields. Presence of stray currents over the PCB surface can generate corrosion problems. The below figure 5 shows severe corrosion damage to micro wave module for 24 GHz. This equipment is built in controlled conditions where water condensation is possible. After few hours of use, severe corrosion was seen on the surface. Figure 5. Stray current corrosion of a micro wave module for 24 GHz used in a control equipment.
Behavior of an active-passive metal: Behavior of metals is divided into three zones. They are as following
1) Active
2) Passive
3) Transpassive
Metal or alloys which initially demonstrates behavior …show more content…
Among all the common metals we take nickel because it has many applications in electronic industry, for an example as a diffusion barrier on electrical contacts and as an electrical conductor on devices. Oxidation of nickel takes place at 100 degrees centigrade and is more sensitive to relative humidity (RH) than to the temperature. Film thickness increases with increase in RH and forms Ni(OH)2 at the surface of NiO film with creation of vacancies in the surface of the oxide. NiP alloys are used as a material for electrical contacts and for metal interconnects. A passivating film is formed at temperature up to 200 degrees centigrade and with thickness ranging from 0.6nm to 1.5nm. Based on study using Auger electron spectroscopy and X-ray photoelectric spectroscopy (XPS), it was found that the oxidation product is an layered structure, which at steady state consists of an inner layer of a nickel phosphate, a middle layer of NiO and an outer layer of Ni(OH)2. These layers are observed by AES depth profiles and by angle-resolved XPS (in the below figure 6). In this Figure 6, we see that at the low, more surface sensitive angle of of 18 degrees, the Ni(OH)2 peak is greatly enhanced and the Ni3(PO4) 2 peak is mostly suppressed compared to the peaks at a takeoff angle of 81 ° at which the signal comes from a greater depth. The peak at NiO is slightly suppressed at 18 degrees but not nearly as much as the phosphate …show more content…
When applied voltage is present even gold is subjected to electrolytic corrosion in micro electric circuits. Generally most of the IC’s applied voltage between conductors is 5-10 V. However, in the presence of sufficient adsorbed moisture on the dielectric, the fraction of the applied voltage that appears across the anode/substrate and cathode/substrate interfaces can be sufficient to sustain an electrochemical reaction. Frankenthal and his co-workers studied the behavior of gold in sulfate solutions containing various amounts of chloride. They found that active transition takes place in all solutions from 1M H2SO4 to saturated NaCl. Figure 7. Anodic polarization curves for Au in 1 M H2SO4 with HCl additions.
Failure mechanism of a discrete semiconductor device was caused by a resistive film of Cr2O3 that had developed between solder connections and metallization to other system components. Figure 8. Anodic polarization curves for Au in unstirred NaCl