Five explanations of the reasons for using black ink on PCB

Since the iPhone (Apple) era, almost all mobile phones have used black pcb circuit boards. What prompted this change? What's special about black pcb?

Statement 1: In the process of washing pcb boards, black pcb boards are most likely to cause color difference. If there is a slight deviation between the raw materials used by pcb board manufacturers and the self-made process, the defective rate of pcb boards will increase due to color difference. So, what should we do?

First of all, I haven't heard about the color difference from the PCB proofing manufacturer. Color difference is not an item of customer assessment, and it is difficult to quantify. In addition, compared with black, other colors are more likely to cause color difference. Because there is one kind of black, try to be as black as possible, while there are many other colors. For example, green includes:

Statement 2: Because the circuit routing of the black pcb circuit board is difficult to identify, it will increase the difficulty of later maintenance and debugging. Generally, if there is no brand of skilled RD (R&D) designers and powerful maintenance teams, the black pcb will not be used easily, This is why only a few high-end brands of high-end series use black pcb boards - it can be said that the use of black pcb proofing is a sign that a brand has confidence in RD design and post maintenance teams, and from the side, it is also a reflection of circuit board manufacturers' confidence in their own strength.

Hate: This statement is just serious nonsense. It seems reasonable.

First of all, Debug has drawings. When debugging the circuit developed by ourselves, you can see the drawings if you can't see them clearly. Besides, who can find a signal depends on the pcb board.

Statement 3: To prevent plagiarism

Brother, have you ever made 4 layers, 6 layers, 8 layers, 10 layers... 20 layers? Even if it is made into green, do you see the line with your eyes?

Do you know a multimeter?

Statement 4: Improve maintenance costs. Although black pcb boards are not necessarily high-end products, the use of black pcb boards reflects the confidence of a manufacturer in its own products and the prudence of its own workmanship. Because the follow-up maintenance of products produced by black pcb boards is relatively difficult, if the quality is not up to standard, the follow-up maintenance cost will be large. Therefore, the products using black pcb boards are generally designed independently, and only high-end products with confidence in product quality can use them. In order to reduce the maintenance cost, the quality control of products using black pcb boards will be more strict, which can improve the utilization of good products of pcb products.

pcb boards

Answer: People who design circuits will not be cheap. It will not increase the maintenance cost for the sake of installation. There are tools for maintenance, not just eyes. If you can see the problem in the circuit, the circuit board factory will be the research object. In general, the masters in the electronic market are all modular replacement. Even if the chip is replaced, they will not observe the pcb routing, mainly relying on tools and experience.

Imagine: Apple maintenance workers in the electronic market can't look at the wire to find the bonding pad.

Are you sure that the green board is used to find lines with naked eyes?

Statement 5: Good heat dissipation? The reason for using black oil is that black oil has better heat dissipation than oil of any other color. All we know is that black objects absorb heat better. In fact, according to the theory of thermal radiation, heat dissipation is the same as heat absorption. The darker the color and the rougher the surface, the better the thermal radiation. So many heat sinks are made into black. The condenser and compressor of the refrigerator are black, which is the reason.

Eh: Black is good for heat dissipation, but your pcb is so hot, and your design is enough.

According to the classical radiation law of physics, the radiation power of all objects is equal to its absorption power, and the absorption power of non black bodies is always less than that of black bodies at the same temperature. Therefore, under the same conditions, compared with the heat dissipation capacity of non black and black objects, the heat dissipation of black objects is significantly faster, and the darker the color, the higher the emissivity and absorption of heat energy.

Finally, black absorbs all the light. Under the same conditions, it naturally absorbs heat more than white. However, according to the classical radiation law, black objects absorb heat faster and dissipate heat faster. Therefore, when it absorbs too much heat, it will give off equal heat, so that it can absorb more heat.

If you need heat dissipation for the pcb, it will be bright copper. It will also use aluminum substrate, which is not black. In fact, compared with other dimensional measures, the color is very small.

If MOSFET needs good heat dissipation, it will enlarge the front pad and remove the solder mask on the back.

1. The cost of black pcb is indeed higher than that of green pcb. Some manufacturers charge for colors.

There are two reasons:

Reason 1: There are many users who choose green, so green is relatively cheap, so you need to charge some fees for other colors.

Reason 2: All boards in batches with black solder resistance color need to be tested! It is difficult to find problems because the processing errors of the surface layer are checked by naked eyes.

In the process of pcb assembly, there is a visual inspection. People's vision is prone to visual fatigue for yellow, red and black. You can inspect 6000 pieces of black pcba on the Foxconn assembly line 12 hours a day.

It is said that apple production line has no visual inspection link (to be verified), and should mainly rely on automatic optical inspection machine (AOI) and non-destructive flaw detector (X-Ray)

2. Because we are used to seeing green pcb boards, and because of coincidence, we chose green paint as the pcb resistance welding material. But if 90% of the world's PCBs are black, it is estimated that people will think black is ugly, while green is taller.

It is estimated that Jobs' obsessive-compulsive disorder is that he likes the strong contrast between black and bright gold of the pad, so he chooses black uniformly. In fact, the iPod is always green.

The use of black PCBs has nothing to do with high-end, but is just a style of designers.

These blade servers of Telecom are priced in tens of thousands or even hundreds of thousands, and are often green.

3. Black pcb is not easy to be found inside the product. This is a fact. If you care about this, just make a reason.

In addition, an open source hardware crowdfunding of "thorough open source" to be launched by Hard Ten is also black. Because, the black pcb convention has become a synonym for quality. Silver tin bright white of chip solder joint and black of printed board and chip package

The circuit board manufacturer, circuit board designer and PCBA processing manufacturer explain the reasons for using black ink on circuit boards in detail.