One, electrical test

PCB in the process of production, hard to avoid the short circuit, open circuit and leakage caused by external factors, such as electrical flaws, coupled with the continuous toward high density PCB, fine spacing and the evolution of multi-level, and failure to timely to bad plate screening out, and let it flow into the process, is bound to cause waste more cost, so in addition to the improvement of the process control, Las técnicas de prueba mejoradas también pueden proporcionar a los fabricantes de PCB soluciones para reducir las tasas de desperdicio y mejorar el rendimiento del producto.

En el proceso de producción de productos electrónicos, la pérdida de costos causada por defectos tiene diferentes grados en cada etapa, y cuanto antes se descubra, menor será el costo de reparación. The Rule of 10 “s is commonly used to estimate The cost of remediation when a PCB is found to be defective at different stages of The process. Por ejemplo, después de la finalización de la producción de placas vacías, si la placa en el circuito se puede detectar en tiempo real, generalmente solo es necesario reparar el defecto, o como máximo la pérdida de una placa vacía; Sin embargo, si no se detecta el circuito, la placa se envía al ensamblador aguas abajo para completar la instalación de las piezas, y el estaño del horno y la refundición por infrarrojos, pero el circuito se detecta en este momento, el ensamblador general aguas abajo preguntará a la empresa de fabricación de placas vacías. para compensar el costo de las piezas, la tarifa de la industria pesada, la tarifa de inspección, etc. If the more unfortunate, the defective board is still not found in the assembly industry’s test, but into the overall system of finished products, such as computers, mobile phones, automobile parts, and so on, then the test to find the loss, will be empty board timely detection of a hundred times, a thousand times, or even higher. Thus, electrical testing for PCB manufacturers is all about early detection of defective boards.

The downstream operator usually requires the PCB manufacturer to perform 100 percent electrical testing and therefore agrees with the PCB manufacturer on specifications for testing conditions and methods, so both parties will first clearly define the following:

1. Test data source and format

2, test conditions, such as voltage, current, insulation and connectivity

3. Production method and selection of equipment

4. Capítulo de prueba

5, repair specifications

There are three stages in PCB manufacturing that must be tested:

1. After etching the inner layer

2. After etching the outer circuit

3, el producto terminado

Cada etapa generalmente tendrá 2 ~ 3 veces de prueba al 100%, elimine la placa defectuosa para un procesamiento pesado. Therefore, the test station is also the best data collection source to analyze the process problem points. According to the statistical results, you can obtain the percentage of open circuit, short circuit and other insulation problems, and then test after reengineering. After sorting out the data, use the quality control method to find out the root of the problem and solve it.

Two, electrical measurement method and equipment

Los métodos de prueba eléctricos incluyen: Dedicated, Universal Grid, Flying Probe, e-beam, conductive cloth, Capacity and ATG-scan MAN are the three most commonly used devices. They are special test machine, general test machine and flying needle test machine. In order to better understand the functions of each device, the features of the three major devices are compared below.

1. Dedicated testing

Fixtures (such as the pins and dials used to test circuit boards) only work with one material number. Boards with different material numbers cannot be tested and recycled. En términos de puntos de prueba, un solo panel se puede probar dentro de los 10,240 puntos y ambos lados dentro de los 8,192 puntos. En términos de densidad de prueba, debido al grosor del cabezal de la sonda, es más adecuado para tableros por encima de la pendiente.

2. Universal Grid testing

El principio básico de la prueba de uso general es que el diseño del circuito de PCB está diseñado de acuerdo con la red. Generalmente, la denominada densidad de línea se refiere a la distancia de la cuadrícula, que se expresa por el paso (a veces también se puede expresar por la densidad del agujero), y la prueba de uso general se basa en este principio. According to the hole position, a G10 substrate is used as a Mask. Only at the hole position, the probe can pass through the Mask for electrical measurement, so the manufacturing of the fixture is simple and fast, and the probe can be reused. The standard Grid fixed large needle tray with many measuring points can be used to produce movable probe needle tray according to different material numbers. As long as the movable needle tray is changed during mass production, it can be used for mass production test of different material numbers. In addition, in order to ensure the circuit system of completed PCB board is unobstructed, it is necessary to conduct Open/Short electrical test on the board with the needle plate of specific contact point on the general-purpose electric measuring machine with high voltage (such as 250V) multi-measuring points. This kind of universal TesTIng machine is called “AutomaTIc TesTIng Equipment” (ATE).

General-use test points are usually more than 10,000 points, and the test density is called on-grid test. If it is used in high-density boards, the spacing is too close, and it has been separated from on-grid design, so it belongs to off-grid test, and the fixture must be specially designed. The test density of the generic test can reach QFP.

3. Prueba de sonda voladora

The principle of the flying needle test is very simple. Only two probes are required to move x, y and Z to test the two ends of each line one by one, so there is no need to make another expensive fixture. Sin embargo, debido a la prueba de punto final, la velocidad de medición es muy lenta, alrededor de 10 ~ 40 puntos / SEC, por lo que es adecuada para muestras y producción de pequeño volumen; In terms of testing density, the flying needle test can be applied to very high density plates (), such as MCM.