**Metal Thickness Test in PCB Design**
There are two primary methods to measure the coating thickness of circuit patterns and through holes:
1. **Non-destructive Method – β Backscattering Method**
2. **Destructive Method – One-Microsecond Method or Cross-Section Method**
**1. Non-destructive Method**
The most widely used non-destructive technique for testing PCB coatings is the β backscattering method. This method is particularly effective for measuring coatings during the electroplating of conductive patterns and through holes, as well as for checking coating thickness after electroplating but before etching begins.
In this method, a radioisotope is mounted on an appropriate detector to emit self-radiation. The detector consists of a radiation source and a receiver. The detector is placed on the metal surface whose coating thickness is to be measured. A portion of the beta radiation emitted from the source interacts with the metal surface and is reflected back to the receiver. As the thickness of the metal coating increases, the intensity of the reflected beta radiation also increases. Using a calibrated scale, a β-ray electronic counter can directly provide the coating thickness in microns.
1: **Non-Destructive Method**
This instrument measures the average coating thickness and is primarily used for assessing the thickness of gold, tin, and tin-lead alloy coatings on copper foil, as well as the copper layer on epoxy resin and the light inhibitor coating on copper foil. To test a wide range of coatings, multiple measurements using beta-ray particles are required. This technology offers a fast, accurate, and non-destructive method for coating thickness measurement, making it widely used in the quality control processes of printed circuit board (PCB) manufacturing. Additionally, it is simple enough for unskilled operators to use.
2: **Destructive Method**
The most commonly used destructive testing technique involves directly measuring the thickness of metal coating microsections, which includes the preparation of metallographic samples and examination under a microscope. The PCB is cut vertically or horizontally, and the visible layer structure is observed under a microscope, allowing for the determination of conductive pattern thickness and the wall coating thickness of through-holes. Typically, the circuit board is cut horizontally with a diamond circular saw, then polished using diamond paste or sandpaper on a grinding wheel polishing machine. The air-dried sample is placed under a microscope at magnifications of 30x to 1000x, with images taken from three different locations on the perforated wall. The average value is usually reported. This microsectioning method for thin coatings can introduce significant errors; for example, with coatings as thin as 1 micrometer, errors may be as large as 50%. However, for thicker coatings, such as those 5 micrometers thick, the error is greatly reduced to around 2%. The advantage of this technique is its applicability to coatings of various types, including through-hole coatings. It also provides additional information, such as the number and type of coatings, uniformity, and details about perforations and undercuts in conductors. However, this method is time-consuming and requires skilled operators for accurate execution.
3: **PCB Perforation Test**
Porosity testing is used to detect inconsistencies in coatings, such as cracks on electroplated surfaces. This test is especially important for gold fingers, as corrosion of the base metal through coating perforations can adversely affect the electrical contact performance of the gold fingers. Therefore, cracks and perforations are the primary focus when testing precious metal coatings.
Several PCB techniques can be employed to detect coating perforations. The most commonly used methods are electrical recording tests and gaseous reagent tests. The gas reagent test involves exposing the electroplated PCB to sulfur dioxide within 24 hours. The sample is placed in a sealed container (capacity: 101 liters), where 0.5 cm³ of water and 100 cm³ of gaseous sulfur dioxide are added. After 24 hours, the container is opened, and 100 cm³ of hydrogen sulfide is injected before sealing the container again. If the PCB coating has porosity, its base metal will corrode, which can be observed either with the naked eye or under a microscope. This perforation test is commonly used to examine gold, lead metal, and tin-nickel alloy coatings on copper and its alloy substrates.
If your have any questions about PCB ,please contact me info@wellcircuits.com
There are two primary methods to measure the coating thickness of circuit patterns and through holes:
1. **Non-destructive Method – β Backscattering Method**
2. **Destructive Method – One-Microsecond Method or Cross-Section Method**
**1. Non-destructive Method**
The most widely used non-destructive technique for testing PCB coatings is the β backscattering method. This method is particularly effective for measuring coatings during the electroplating of conductive patterns and through holes, as well as for checking coating thickness after electroplating but before etching begins.
In this method, a radioisotope is mounted on an appropriate detector to emit self-radiation. The detector consists of a radiation source and a receiver. The detector is placed on the metal surface whose coating thickness is to be measured. A portion of the beta radiation emitted from the source interacts with the metal surface and is reflected back to the receiver. As the thickness of the metal coating increases, the intensity of the reflected beta radiation also increases. Using a calibrated scale, a β-ray electronic counter can directly provide the coating thickness in microns.
1: **Non-Destructive Method**
This instrument measures the average coating thickness and is primarily used for assessing the thickness of gold, tin, and tin-lead alloy coatings on copper foil, as well as the copper layer on epoxy resin and the light inhibitor coating on copper foil. To test a wide range of coatings, multiple measurements using beta-ray particles are required. This technology offers a fast, accurate, and non-destructive method for coating thickness measurement, making it widely used in the quality control processes of printed circuit board (PCB) manufacturing. Additionally, it is simple enough for unskilled operators to use.
2: **Destructive Method**
The most commonly used destructive testing technique involves directly measuring the thickness of metal coating microsections, which includes the preparation of metallographic samples and examination under a microscope. The PCB is cut vertically or horizontally, and the visible layer structure is observed under a microscope, allowing for the determination of conductive pattern thickness and the wall coating thickness of through-holes. Typically, the circuit board is cut horizontally with a diamond circular saw, then polished using diamond paste or sandpaper on a grinding wheel polishing machine. The air-dried sample is placed under a microscope at magnifications of 30x to 1000x, with images taken from three different locations on the perforated wall. The average value is usually reported. This microsectioning method for thin coatings can introduce significant errors; for example, with coatings as thin as 1 micrometer, errors may be as large as 50%. However, for thicker coatings, such as those 5 micrometers thick, the error is greatly reduced to around 2%. The advantage of this technique is its applicability to coatings of various types, including through-hole coatings. It also provides additional information, such as the number and type of coatings, uniformity, and details about perforations and undercuts in conductors. However, this method is time-consuming and requires skilled operators for accurate execution.
3: **PCB Perforation Test**
Porosity testing is used to detect inconsistencies in coatings, such as cracks on electroplated surfaces. This test is especially important for gold fingers, as corrosion of the base metal through coating perforations can adversely affect the electrical contact performance of the gold fingers. Therefore, cracks and perforations are the primary focus when testing precious metal coatings.
Several PCB techniques can be employed to detect coating perforations. The most commonly used methods are electrical recording tests and gaseous reagent tests. The gas reagent test involves exposing the electroplated PCB to sulfur dioxide within 24 hours. The sample is placed in a sealed container (capacity: 101 liters), where 0.5 cm³ of water and 100 cm³ of gaseous sulfur dioxide are added. After 24 hours, the container is opened, and 100 cm³ of hydrogen sulfide is injected before sealing the container again. If the PCB coating has porosity, its base metal will corrode, which can be observed either with the naked eye or under a microscope. This perforation test is commonly used to examine gold, lead metal, and tin-nickel alloy coatings on copper and its alloy substrates.
If your have any questions about PCB ,please contact me info@wellcircuits.com
