How important is "100% full inspection" for quality in PCB prototyping?

1. What are full and spot checks?

Full testing, that is, all testing, testing each board in each batch to ensure that the whole batch of finished products meet the standard rate of 100%.

Sampling test, in the same batch of prototype circuit boards, random sampling of a certain number of samples for testing, if the sample test is not a problem, then the default batch of finished products meet the standard rate of 100%.

Why does Jinghongyi PCB insist on 100% full test, in principle it does not need "random test"

Because of the sampling mechanism itself, the risk of broken board is high. When users get the board, they find that the sample board is short-circuited and open, and they have to scrap it. Therefore, in order to avoid unnecessary losses to customers, Jinghongyi PCB insists on the default 100% full test to ensure the high quality and high yield of each batch of finished boards.

2. How to ensure the speed and quality of the full measurement under the premise of shortening the delivery time?

Jinghongyi PCB has started to speed up the delivery of small batches long ago, with double-sided PCBs of 5-10 square meters and 3 days (72 hours) delivery, and still maintains 100% full measurement.

Question: How to ensure the speed of the whole measurement and the rate of the product meeting the standard when the delivery time is accelerated?

Answer: Jinghongyi PCB has introduced several flying needle testing machines, AC8 brusher (flying needle accelerator) and new testing equipment to meet the different test volume pressure of PCB prototype manufacturing orders and batch orders, so as to fully meet 100% of the total test requirements and ensure 100% of the finished products meet the standard rate.

3. Introduction to Flying Needle Machine Testing

Flying needle tester uses 4, 6 or 8 probes to test high voltage insulation and low resistance conduction of circuit board (test circuit opening and short circuit) without testing fixture. It is suitable for testing small batch sample board. Generally, the method of "truth value comparison and location" is used to monitor the testing process and fault points in real time, so as to ensure the accuracy of the testing.

The general procedure of the test of the flying needle machine is as follows:

After reading the data from the flying needle workstation and converting the test files of the flying needle tester, the first piece is produced, the capacitance and resistance data are collected, and the production begins.

The characteristics of flying needle machine test:

1). Flying needle machine must first learn the standard board and read in the standard capacitance value of each network.

2). First, the capacitance method is used to test the capacitance. When the measured capacitance is not within the qualified range, the resistance method is used to confirm accurately.

Advantage:

1). The test density is high, the minimum Pitch can reach 0.05 mm or even smaller.

2). Fixture-free cost

3). More suitable for prototype manufacturing

4). Low cost of prototype production

Disadvantages:

1). High breakage rate of test needle

2). Test speed is relatively slow

3). Voltage withstand cannot be tested, high-level high-density board testing has greater risk.

4). Not suitable for batch testing

5). Test accuracy is lower than test stand

6). Return orders need to be charged again

4. Introduction to Test Frame (PCB Fixture)

The test stand test method is one of the widely used circuit board test methods in PCB industry. It relies on the test stand (i.e. fixture) to test whether there is a short circuit between different PCB network routes, whether the same PCB network is open to each PAD, whether the through hole is open, and whether the insulation strength test and impedance test can also be carried out. Its remarkable characteristic is that the test speed and accuracy are very high.

Generally speaking, the test stand tests the qualified product circuit boards, that is to say, the quality is up to the standard.

Testing procedure of test stand:

Test stand on board
Simulating Full Short Circuit Test with Aluminum Sheet
Simulating Full Open Circuit Test with Conductive Film
Learning Test of Fine Product Board
Ensure that the probe (i.e. loop) of the test stand is not abnormal
Feeding production

Advantage:

1). High test accuracy
2). Fast testing speed, suitable for batch testing
3). Two batch tests, only one test stand, lower cost
3). One-time charges, no extra charges for return bills

Disadvantages:

1). For the first time, we have to pay a fee to make the test stand. The prices vary from factory to factory.

2). Not suitable for PCB prototype order testing

5. Introduction of AC8 Brush Machine (Flying Needle Accelerator)

AC8 brush machine (flying needle accelerator), which can speed up the speed of flying needle testing, is an electromechanical scanning device, which can increase the production of flying needle testing by 2-7 times (depending on the type of PCB), but can not be used for testing alone.

Its technical basis is the capacitance method test which is widely certified by the industry (capacitance method: using mechanical contact, brushing the circuit board lightly). The problem network scanned by AC8 is duplicated with the connection of the flying needle tester to identify the PCB problem points.