Question 1

What does the term “X-out” mean in the PCB industry?

Accepted Answer

In the PCB industry, the term “X-out” also known as “Cross-board” and “X-board”. It stands for the defective boards in PCB panels, and X marks are usually marked on the top.
Normally, the SMT factory will not allow X-out boards appear in PCB panels, because it cause the loss of efficiency during the process of SMT. However, the X-out boards is inevitable while producing PCBs, the more PCBs in one single panel, the more likely X-out boards appear.
The Acceptable Quality Level (AQL) for X-out boards in the PCB industry, generally, the number of X-out boards must be less than 20% of the number of PCBs in a panel. That is, in a panel with 4 pieces of PCBs, only allowed 1 X-out board in it. In a panel with 8 pieces of PCBs, only allowed 2 X-out boards. And the total amount of X-out boards must be less than 10% of total PCB shipments.
When about to ship the PCBs, must be assured that in each vacuum bag, the position of X-out boards must be the same position in each panel. If the X-out boards less than the quantity of the whole package, it must be packed in the mantissa box, and clearly marked with the total quantity of PCBs and X-out boards and relevant information.
If the buyers allow X-out boards to exist in PCB panels, the SMT factory can skip the X-out boards without doing SMT process by modifying the SMT program or by identify the bad marks on PCBs. But it will cause the SMT efficiency loss.
If the buyers will NOT allow X-out boards to exist, it means the PCB manufacturers are forced to produce more PCB panels, in order to eliminate the PCB panels, which has X-out boards in it. Therefore, the purchase cost will increase, but the SMT process will achieve the maximum of efficiency.

Question 2

The pro and con of the gold finger and its application on the PCB.

Accepted Answer

Gold finger is the metal connector on the PCB, and gold finger is also known as Gold tips or Gold tabs.
Gold fingers are the gold plated connectors on the edge of PCB that arranged like fingers. During PCB manufacture process, gold finger will be coated with a layer of gold through a special process on the copper cad lamination. However, today, many PCB designer has replacing the surface finish of gold finger by tin plating.
For PCB designer, the aim of gold finger is to connect the PCB by compressing the corresponding slots with connector, which allows its to communicate with one device to another.
The advantages of using plating gold on gold fingers for the PCB: The gold finger can resist oxidation and it is durable with high conductivity.
The disadvantages of gold finger on the PCB: it has relatively uneven surface, the needs of connecting line and the price of gold finger is extremely expensive.
The difference between applying immersion gold and plating gold on the gold fingers is that immersion gold is easier to solder compare to plating gold and will not affect the signal, it is also hard to get oxidized. However the immersion gold is less durable.

Question 3

The advantages/disadvantages about SMT

Accepted Answer

SMT is a technology that uses electronic components to mount on the PCB.
SMT is to print solder paste on pad then place the electronic components on it. Next, we heat up to liquefy the solder paste and wait for cool down. After cool down, those electronic components will be mounted on the PCB.
SMT can make electronic product’s design become more delicate because the size of electronic components is small, this can reduce the size of PCB significantly.
SMT is suitable for PCB mass production because SMT supports automated production also the SMT production is a lot more stable than DIP.
SMT can reduce the labor cost and operating hours for manufacturing the PCB.

Question 4

The differences and application of hard gold plating and soft gold plating.

Accepted Answer

Plating gold is a type of PCB surface finish, also known as nickel gold electroplating. In the PCB manufacturing process, plating gold is to deposit a layer of gold plated over a barrier coat of nickel by electroplating.

Plating gold can be divided into ''hard gold plating'' and ''soft gold plating''. The PCB manufacturer has to take the characteristic of the two types of gold into consideration during PCB designing.

In PCB gold plating process, hard gold plating is also referred to as a plating alloy. It has been alloyed with other elements which makes it harder, whereas the soft gold plating is pure gold.

Plating gold application in PCB manufacturing. Hard gold plating is suitable for use in places where the force of friction is needed such as gold finger, keypad. Soft gold, is typically used for aluminium or gold wiring on COB (Chip On Board).

Question 5

Why does V-CUT will be added during PCB design?

Accepted Answer

Because the strength and hardness of PCB.
After finishing the pc board assembly, in order to fit the PCB into the end product. The PCB manufacturer will design V-Cut to de-panel the PCB
Those dividing lines that were cut by cutter on the PCB is called V-CUT and it is commonly seen between break-away rail and unit on PCB.
It is literally impossible to de-panel PCB with your hands.
Even if you do break the PCB manually, the electronics circuit board parts will be damaged.
When bending the PCB, the application of the force will cause PCB deformation which might result in the electronics circuit board parts cracked.
If thickness of PCB is too thin, we do not suggest to do V-CUT because it will damage PCB structural.

Question 6

Why does long stored PCB need to be baked before assembly or running through reflow oven?

Accepted Answer

The purpose of baking is to remove the moisture from the PCB.
No matter the PCB is at production site or still in vacuumed package, both would increase the risk that PCB can absorb moisture.
If PCB is stored at a bad storage condition or over storage period, these would also make the PCB absorb moisture easily.
The high temperature would cause inner board moisture evaporation when assembly the damp PCB.
The PCB will have blister or delamination due to steaming.

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