BGA chip is very small, how to solve the wiring problem of circuit board design

BGA chip is very small, how to solve the wiring problem of circuit board design

Recently, I often encounter some purchases of circuit boards. When they find me, I am very entangled and told me: Many circuit board manufacturers can’t handle the PCBs designed by their engineers, or they can’t do it beyond the production process, or the engineer’s design is unscientific...and They do not know the technology and the PCB production process, so they are in a dilemma. They don’t know how to communicate with the PCB factory, nor can they express the designer’s ideas and get effective suggestions for improvement...

Hearing this, my interest immediately soared. The first reaction was to ask them to send the drawings over. My son/Miss had to go through it in person to see which design master had a new trick?

After reading the (PCB multi-layer board) drawings, I discovered that it is another common and old problem, but it is caused by many designers not understanding the PCB factory process!

First, let me talk about the problems I saw:

1. The BGA ball center pitch is 0.4mm, and the design engineer has designed the trace between the BGA pads.

2. Circuit board vias are designed between the four BGA pads.

Next, I will tell you why the PCB factory saw such a design and could not make it:

A: The distance between BGA sphere centers is 0.4mm, and the minimum BGA is 0.2mm, so that the BGA pad pitch is only 0.2mm.

If the wire is routed, the minimum limit of the wire is 3mil, which is 0.075mm. In this way, the distance between the line and the pad is only left:

(0.4-0.2-0.075)÷2=0.0625mm, only 2.46mil. This spacing will definitely not work!

Here comes the focus, I will emphasize the two extreme limits of PCB production:

One: The minimum BGA clamp line is 3mil, and the minimum distance between the BGA clamp line and the pad is 3mil.

Two: The limit distance from the via to any pattern (line, pad, large copper):

The outer limit distance: 6mil. The limit distance of the inner layer of the circuit board: 8mil.

Someone may ask: Why is the inner layer spacing larger than the outer layer? Because, in the PCB production process, the deviation of the inner lamination alignment will be greater!

Having said this, design engineers should be confused: Now that there are more and more 0.2mm BGA chips, is there no way?

The answer is yes: there must be! With the advent of the intelligent age, electronic devices are becoming more and more sophisticated. These are all problems that must be solved! Next, I will tell you the solution: design the hole in the disk and use the resin plugging process!

Hole in the disk, as the name implies: punch a hole in the pad! So what kind of circuit board manufacturing process is the hole in the disk? Here I will introduce it in detail!

The manufacturing process of the hole in the disk includes: drilling, electroplating, resin plugging, baking, and grinding. First, drill holes. The holes here are generally laser holes.

The minimum limit of the mechanical hole is 0.15mm, if it is 0.1mm, the laser must be used to drill the hole.

After the holes are drilled, the holes are electroplated and metalized, and then the holes are plugged with resin, baked, and finally polished to smooth them. The resin after the smoothing does not contain copper, so another layer of copper is needed to turn it into PAD, these processes are done before the original PCB drilling process, that is, the holes of the fortress hole are processed first, and then the other holes are drilled, according to the original normal PCB factory process.

Generally, the boards with holes in the design disk will have the blind holes or buried holes we mentioned.

For example, a (PCB multi-layer board) four-layer board: 1 layer-2 layers to make holes in the disk, and then 2 layers-1 layer wiring out, and then 1 layer-4 layers can also be punched and wiring.

In this way, a four-layer first-order HDI board of 1-2,1-4 or 1-2,1-4,3-4 is formed.

Of course, (PCB multi-layer board) six or eight layer boards can also be designed in the same way.