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PCB and PCBA design considerations

Product background

This product is a new product produced by us, and this production is a sample. Communicating with the customer since September 20, the customer is an Argentinean service and technology company, this company specializing in lubrication system engineering.

 

This product is an electronic circuit board in a refrigeration system tailored to a customer in Brazil. The product is currently in the research and development stage, so from September last year to now, the design has been changed 3 times, and 10 samples of this time have been produced.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PCBA product introduction

Because of the special nature of the product's work, the board is a more complex 4-layer board. The exterior design is in line with the conventional green oil and white silk screen. For subsequent assembly, there are 4 large PTH holes, they will be used for screw fixation. The small vias on the surface are all covered with solder oil.

 

Features of PCB:

It is particularly worth mentioning thing is there are multiple buried holes inside this small PCB. So what is a buried hole?

 

Generally, we often see there are three types of PCB vias, as following:

 

Through Hole: 

Plating Through Hole abbreviated as PTH, this is the most common one, you only need to pick up the PCB and face the light, the hole that can see the bright light is the "through hole".

 

This is also the simplest type of hole, because when making it, you only need to use a drill or a laser to directly drill the circuit board, and the cost is relatively cheap. But on the other hand, some circuit layers do not need to connect these through holes.

 

 For example, we have a six-story house. I bought its third and fourth floors. I want to design a staircase inside that only connects the third floor to the third floor. It is fine between the fourth floor. For me, the space on the fourth floor is invisibly used up by the original staircase connecting the first floor to the sixth floor.

 

So although through holes are cheap, they sometimes use up more PCB space.

 

Blind Via Hole: 

Blind Via Hole, it will connects the outermost circuit of the PCB with the adjacent inner layer by plating holes. Because the opposite side cannot be seen, it is called "blind via".

 

In order to increase the space utilization of the PCB circuit layer, a "blind via" process has emerged.

 

This production method requires special attention to the depth of the drilling (Z axis) to be just right. This method often causes difficulties in electroplating in the hole, so it is almost used by no manufacturer; it is also possible to place the circuit layer, and needs to be connected in the individual circuit layer in advance.

 

At that time, the holes should be drilled first, and then glued together, but a more precise positioning and alignment device is required.

 

Buried hole:

Buried hole, the connection of any circuit layer inside the PCB but not conducting to the outer layer.

 

This process cannot be achieved by drilling after bonding. It must be drilled on the individual circuit layers. After the inner layer is partially bonded, it must be electroplated before it can be fully bonded. Compared with the original "through hole" and "Blind holes" take more time. 

 

So the price is the most expensive. This process is usually only used for high-density (HDI) circuit boards to increase the usable space of other circuit layers.

 

The different holes are shown below, can learn clearly.

 

 

Preparation before production

1. Silk screen problem

When the Working gerber was ready to confirm with the customer, the customer failed because there was no logo silk screen. But our display is silkscreened with logo. As the point by arrow below, but the customer side no.

 

 

After discussing several rounds, it turns out that the two sides read gerber in different ways, in our way it hides a layer. Found the problem, we quickly produced PCB and waited for production. The correct logo is shown below:

 

2. Orientation issues

This product is a new product for our company, so the IQC department conducts regular pad inspection on this product. At first, I found that the drawings used for SMT were incomplete, and the IC had no direction.

 

 

After communicating with the client, the client said that his design is directional. As shown by the arrow in the figure below (the left side is our company’s mounting drawings, and the right side is the original design of the customer)

 

 

After discuss with customer many time, it turned out that Gerber missed a layer when exporting.

 

In fact, many chips can confirm the direction according to the schematic diagram, but in order to ensure that the principle is the same as the customer's design, we choose to confirm with the customer if there are any doubts.

 

After updating the information and completing the direction confirmation problem, we found another problem.

 

3. Wrong chip size

As shown in the figure below, the pins of the chip do not match the pads on the PCB

 

 

When we gave feedback to the customer, the customer discovered that when they updated the design, they only updated the gerber without updating the corresponding bom.

 

As I said before, this product is in the design stage, so the gerber and information have been updated several times. Fortunately, we have the stage of IQC verification, otherwise it would be very troublesome to suspend refueling in the middle of production.

 

Fortunately, we have a complete supply system, and quickly updated the correct components to complete this product.

 

Words form customers:

 

The production process went smoothly and there were no more problems. But the customer said it was the first time he designed PCB products with buried hole, in order to reduce the size.

 

He will tell me the result after the test. He said that through this cooperation, he learned about our company's serious attitude towards products, and he hoped to have the opportunity to continue to cooperate in the future.

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