Q: Talk about “Bow and Twist” of PCB from IPC-6012E

<img style="display: block; margin-left: auto; margin-right: auto;" src="https://www.explus.com.tw/upload_files/Knowledge/Based%20on%203-4-3%20%E2%80%9CBow%20and%20Twist%E2%80%9D%20in%20IPC-6012%2C%20what%E2%80%99s%20the%20acceptance%20criteria%20in%20terms%20of%20%20PCB%20warpage%20for%20printed%20circuit%20board%20that%20use%20for%20surface%20mount%20components.png" alt="" width="523" height="438" /> Defined in IPC-6012E 3.4.3 Bow and Twist , unless otherwise specified in the procurement document, when designed in accordance with IPC-2221, the printed board shall have a maximum bow and twist of 0.75% for printed boards that use surface mount components and 1.5% for all other printed boards. In other word, PCB warpage under 0.75% are accepted according to IPC standard. Can twisted or bowed board be corrected (bent back) manually? No, if bending the PCB manually might worsen PCB warpage. Does PCB mounting process be affected by PCB warpage? Basically, PCB assembly supplier refer to IPC-6012E standard as well, if client has special requirement, they will produce carrier to support the PCB during the process. Also, SMT equipment, in the MOUNTING section, must have a splint design on the conveying track. So if the warpage within standard, the PCB could be mounted without problem.

Question 1

Talk about “Bow and Twist” of PCB from IPC-6012E

Accepted Answer

Defined in IPC-6012E 3.4.3 Bow and Twist, unless otherwise specified in the procurement document, when designed in accordance with IPC-2221, the printed board shall have a maximum bow and twist of 0.75% for printed boards that use surface mount components and 1.5% for all other printed boards. In other word, PCB warpage under 0.75% are accepted according to IPC standard.

Can twisted or bowed board be corrected (bent back) manually?
No, if bending the PCB manually might worsen PCB warpage.

Does PCB mounting process be affected by PCB warpage?
Basically, PCB assembly supplier refer to IPC-6012E standard as well, if client has special requirement, they will produce carrier to support the PCB during the process. Also, SMT equipment, in the MOUNTING section, must have a splint design on the conveying track. So if the warpage within standard, the PCB could be mounted without problem.

Question 2

Solder Mask Is the Layer of Copper Protection

Accepted Answer

After copper plating and PTH process, outer layer trace is following as the next step. However, outer layer trace shares the same process of inner layer trace. For understanding more, please read below article.
https://www.explus.com.tw/faq/What-Are-The-Steps-of-PCB-Inner-Layer-Process.html

After all copper trace is done, we have to protect copper trace from oxidation. And that is what solder mask is printed on PCB for.

Similar to lamination, PCB manufacturer scrubs the PCB surface and then applies micro-etching to increase the adhesion when solder mask ink is printed on the surface. After printing solder mask ink, curing is applied to solidify the ink as the copper trace protection layer.

Green solder mask may be the most common color you can see on PCB. However, do you know what different colors of solder mask that are applied on PCB?

Question 3

What is impedance control? - Part.3

Accepted Answer

The impedance of the PCB trace will be determined by its resistance, inductance and conductance. The PCB impedance ranges from 25 to 120 ohm. The main factors that affect the impedance of the PCB traces are as below:

1. Trace width / thickness;
2. The dielectric constant;
3. Thickness of the medium;
4. The thickness of the pad;
5. The path of the ground line;
6. The traces around the trace

PCB transmission lines usually consist of traces, one or more reference layers, and insulating materials. Traces and slabs constitute the control impedance.

Question 4

Introduce COB's bonding wire and its pulling force

Accepted Answer

The previous article has introduced what COB is and the process of COB. Under the process, what kind of bonding wire and tensile test does COB have?
After the COB die is adhered and baked, the wire bonding process is followed. The COB process is different from IC packaging. It is gold wire for IC, and aluminum wire for COB. Therefore, the shape of the solder joint will be different, and secondly, the tensile force of the solder wire will also be different.

Wire Bonding

According to the shape of the solder joint, the wire bonding process can be divided into two types: "Ball Bond" and "Wedge Bond". COB usually uses aluminum wire (Al wire) so it will be Wedge Bond. However, according to experience and data, the strength of ball welding is better than that of wedge welding, but the "gold wire" is also more expensive.

Wire Pull Test

In the IC packaging process, the quality of the bonding wire is usually judged by three methods: Wire pull, die shift, and Ball Shift. Generally speaking, most COB The manufacturing process will only test the wire tension, which can measure whether the strength of the solder joints on the PCB is sufficient. The COB wire tension requirement is usually only greater than 3g according to the IPC specification (TM-650 2.4.42.3).

Question 5

Where are printed circuit boards used? VI

Accepted Answer

PCBs are used in many different sectors. Today we are talking about some applications in industrial products. PCB are widely used in the industrial part.

The PCBs used in the industrial sector often need to be especially high-powered and be durable enough to withstand the harsh conditions that exist in industrial facilities. PCBs may need to be resistant to rough handling, vibrating machinery, extreme temperatures or harsh chemicals. To meet this need for durability, industrial PCBs may be made with durable metals or thermal-resistant materials and be thicker than other kinds of PCBs.

Manufacturing equipment
Power equipment
Measuring equipment

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Question 6

Panel Copper Plating → PTH (Plated Through Hole)

Accepted Answer

The step follows drilling hole is copper plating.
Except those drilling holes for tooling purpose, the rest of the drilling-hole wall will be plated with copper as for the purpose of connection of trace in different layers or for those DIP components.

By blocking the holes and areas with no needs of copper, copper plating is applied not only on the drilling-hole wall but also on the whole PCB.
For requirement of finished 70um, normally PCB vendor takes 35um material and do copper plating to be 70um.

Question 7

What is E-TEST?

Accepted Answer

How does PCB manufacturer ensure the bare PCB is within standard before delivery?

Once of tests it will be conducted is “E-test” which is also known as electricity test. The main purpose of E-test is to make sure there’s no open circuit and short circuit.

When it’s sample production, most of time the manufacturer will use “Flying Probe test” for E-TEST. Even though flying probe test is comparatively time consuming in terms of production efficiency but it makes sense especially the project is still on pilot phase.

Once the project enters Mass Production, usually the PCB manufacturer will produce specialized tooling for each project. No matter it’s “Flying probe test” or “tooling test”, the main target is to detect NG circuit during “E-TEST STAGE” and ensure the quality is within client’s standard.

What is HiPot test?

Question 8

What is impedance control? - Part.2

Accepted Answer

Last time we have briefly introduced the PCB data transmission and impedance control. And the transmission method can be divided in two types – Single-ended and Differential signal. Both have their own pros & cons, and which method to use for transmission depends on the functionality of the IC as well as electrical considerations. Nowadays, differential transmission has become the mainstream of high-speed transmission.

What is Single-Ended Signal
Single-ended signals generally refer to all kinds of signals that can transmit messages with one transmission trace (signals on PCB are mostly this kind). Its biggest pro is that the impedance is easy to control.

What is Differential Signal

Differential signals use two single-ended signal traces (Positive and Negative ) to transmit signals at the same time. These two signals should have two features:
1. Same voltage amplitude
2. The phase of the signal is opposite, that is, one positive and one negative.

What is impedance control? - Part.1

Question 9

What is Glass Transition Temperature, also known as TG?

Accepted Answer

Sometimes you can see TG150/TG170, etc. on the PCB material. What does this TG mean?

TG(Glass Transition Temperature) is one of the most important characteristics of all plastic and epoxy resin materials. In fact, TG(Glass Transition Temperature) value is also one of the quality indicators of glass fiber for PCB.
When the temperature is lower than the glass transition temperature (TG), the plastic enters glassy state which is rigid but with brittle characteristics. Just like the characteristics of glass, it is hard but easily brittle.
When the temperature is higher than the glass transition temperature (TG), the plastic parts will show a soft and flexible rubbery state. Therefore, the glass transition temperature (TG) is generally the temperature at which the plastics undergo a phase transition from the glassy state to the rubber state.

As PCB’s TG(Glass Transition Temperature) increasing, the heat resistance, moisture resistance, chemical resistance, and resistance stability characteristics of PCB prodution will be strengthened and improved. The higher the TG(Glass Transition Temperature) value, the higher temperature PCB can endure, especially in the lead-free manufacturing process, where there are more applications of high TG(Glass Transition Temperature).

High TG(Glass Transition Temperature) refers to high heat resistance. The development of high functionalization and high multi-layering requires higher heat resistance of PCB substrate materials as an important guarantee. The emergence and development of high-density mounting technologies represented by SMT and CMT have made PCBs increasingly require specifications with high heat resistance of substrates in terms of small apertures, fine lines, and thinning.

Thus, regards PCB production, the difference between FR-4 and high TG FR-4 is that in a high temperature state, especially when heated after moisture absorption, the material’s mechanical strength, dimensional stability, adhesiveness, water absorption, thermal decomposition, and thermal expansion.

Question 10

Where are printed circuit boards used? V

Accepted Answer

Today we are talking about some applications in military products. Military-grade PCBs carry stringent performance, sourcing, and manufacturing requirements that are encoded in a number of standards, such as IPC-A-610E Class 3, MIL-PRF-31032, MIL-PRF-55110, etc. These standards specify performance requirements for high-performance electronic products.

These military printed circuit boards will often be subjected to high pressures and stresses, meaning they will frequently require high-temperature substrates like temperature-resistant laminates, copper or aluminum. Military PCB manufacturers must produce PCBs that will resist heat-induced oxidation and effectively dissipate heat in a low-weight design.

• Auxiliary power units for radar control systems
• Radio communications systems
• Control tower systems
• LED lighting systems
• Underwater navigation systems
• Jet instrumentation
• Jamming systems

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