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, Le tecniche di test avanzate possono anche fornire ai produttori di PCB soluzioni per ridurre i tassi di scarto e migliorare la resa del prodotto.

Nel processo di produzione di prodotti elettronici, la perdita di costo causata da difetti ha gradi diversi in ogni fase e prima si scopre, minore è il costo della riparazione. La regola dei 10 “s è comunemente usata per stimare il costo della riparazione quando un PCB risulta difettoso nelle diverse fasi del processo. Ad esempio, dopo il completamento della produzione del piatto vuoto, se la scheda nel circuito può essere rilevata in tempo reale, di solito è sufficiente riparare il difetto, o al massimo la perdita di un piatto vuoto; Tuttavia, se il circuito non viene rilevato, la scheda viene spedita all’assemblatore a valle per completare l’installazione delle parti e lo stagno del forno e la rifusione IR, ma il circuito viene rilevato in questo momento, l’assemblatore generale a valle chiederà all’azienda produttrice di schede vuote per compensare il costo delle parti, la tassa dell’industria pesante, la tassa di ispezione, ecc. 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, condizioni di prova, come tensione, corrente, isolamento e connettività

3. Production method and selection of equipment

4. Capitolo test

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, il prodotto finito

Ogni fase avrà solitamente 2~3 volte di test al 100%, escludendo la piastra difettosa per l’elaborazione pesante. 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

I metodi di prova elettrici includono: 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. In termini di punti di test, un singolo pannello può essere testato entro 10,240 punti ed entrambi i lati entro 8,192 punti. In termini di densità di prova, a causa dello spessore della testa della sonda, è più adatto per schede sopra il passo.

2. Universal Grid testing

Il principio di base del test di uso generale è che il layout del circuito PCB è progettato secondo la griglia. Generalmente, la cosiddetta densità di linea si riferisce alla distanza della Griglia, che è espressa da Pitch (a volte può essere espressa anche dalla densità dei fori), e il test di uso generale si basa su questo 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. Prova della sonda volante

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. Tuttavia, a causa del test dell’endpoint, la velocità di misurazione è molto lenta, circa 10~40 punti/SEC, quindi è adatta per campioni e produzioni di piccoli volumi; In terms of testing density, the flying needle test can be applied to very high density plates (), such as MCM.