SMT, PCB Electronics Industry News

Which PCB testing method is better for you?

Nov 05, 2019

Very often, customers ask details about what kind of testing do we use? How do we charge it? Do I have to pay every time or only for the first time? Is this testing safer and better than other one? etc

In this blog, let's discuss the various kind of testing and their advantages and disadvantages. Some of them are mandatory, some of them are optional;  Some of them are fast, some are slow; some of them are more reliable, and some not. Hope you will have a better understanding about various kinds testing and make better decision on your next PCB order.

1. Electrical Test Fixture

A test fixture is a device used to test printed circuit boards from circuit opens or circuits shorts.

Application: Mass production, Regular PCB production

Advantages: 

1. It is only one time cost, once you pay for it, all future repeat orders will be free of testing cost; 

2. Testing speed is fast, it only take about 5 seconds or so; 

3. Long time lasting, with proper maintenance, you can use it for 5 years or even more

4. Easy to use, you don't need to input gerber data, so the chance of making mistake is rare

Disadvantages: 

1. The cost is high, normally from USD 100-USD 500, depending on the complexity of your boards; 

2. Making a fixture takes normally 2-3 days, thus not suitbale for fast production service.

3. It is easy to break or bend, you have to carry it with care, and check it everytime before using it

4. Once fixture is finished, you can not change it; If a minor change happens to gerber, it means your fixture is useless.

2. Fly Probe Tester

A fly probe tester is a machines to test printed circuit boards from circuit opens or circuits shorts.

Application: Prototype, Samples, and smaller quantity production

Advantages: 

1. The starting cost is relatively low, ranging from USD 10-USD 100, depending on quantity and density.

2. Ready to use anytime;  unlike testing fixture, you don't need to wait several days to use it, you can use fly probe tester immediately, anytime.

3. Easy to adjust and upgrade. Many times you find a mistake in your gerber in the last minute, no problem, just send over your new files, and  there is no material wasted, no extra cost charged

Disadvantages: 

1. It is a eveytime cost service, each time you order the same PCB, you pay this testing service

2. Testing speed is slow, it might take 10 minutes, 30 minutes or even hours, based on on the complexity of your boards

3. Not easy to use, you have to input gerber data in the correct format, so the chance of making mistake is bigger

Besides, as fly probe tester are becoming more and more sophisticated, you have to train workers to use it properly.

3. AOI Testing

AOI stands for Automatic optical inspection.

Nowadays, more and more PCB factories are using AOI testing method.  AOI is a key technique used in the manufacture and test of printed circuit boards, it enables fast and accurate inspection to ensure that the quality is high and without manufacturing faults.

Application: Multi-layer PCB, HDI PCB, and high density PCBs

Advantages: 

It inspects various PCB defects like circuit shorts, opens, line width violations, missing pad, hole breakage, spacing violation, etc

The inspection is very reliable and repeatable, it prevents and stops 100% of bad boards.

AOI is used in the middle of production, normally before solder mask process, so you can pick the bad boards and save production cost.

Disadvantages: 

AOI machines are quite expensive, and not every factory can afford them.

AOI machine is very sophisticated, and it takes much time to learn how to operate them properly.

They are often used in high density or multi-layer PCBs, it is not necessary to use on simpler 1-2 layer ones.

4. Visual Inspection

Visual inspection, uses either or all of raw human senses such as vision, hearing, touch and smell, is a common method of quality control. It is normally used in FQC (Final Quality Control)process before shipping boards to customers. Sometimes, if boards are quite simple with fewer circuits, less PADs, bigger holes, it can also replace electrical testing to save cost.

Application: Simple boards(1 layer or 2 layer), FQC Process

Advantages: 

1. Cost is free, Visual inspection is standard procedure in PCB production, no matter you ask for it or not, PCB factories will still do it

2. Speed is fast, workers can visual inspect a pcs of board in 5-10 seconds.

3. Experienced workers can inspect lots of defects, like scratches, circuit opens, shorts, hole damages, silk screen misplaced, PAD mismatch,  and then repair them.

Disadvantages:

1. It is easy to make mistakes, human workers are easy to get tired, and mistakenly put bad boards with good ones.

2. If boards are covered with white solder mask or black one, it is more difficult to identify defective boards.

3. Although Visual inspection can tell many defects,  yet it is not possible to check holes, vias, and inner layers.

4. Factories need lots of time and energy to train workers to make ensure they understand IPC standard, and identify good ones from bad ones.

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