BGA chip is very small, how to solve the wiring problem of circuit board design
Recently, I have often encountered some purchases of PCBs. When I found myself, I was very tangled to tell me that many of the PCBs that their engineers made were uncertain, either because they were beyond the production process or because their engineers were not scientifically designed. But they don't understand technology and PCB production technology, so both sides are in a dilemma. They don't know how to communicate with the PCB factory, nor can they express the designer's ideas in order to get effective suggestions for improvement...
When I heard this, my interest soared. The first reaction is to have them send the drawings. Ben / Miss wants to see them personally and see what new ideas God has put forward.
After reading the drawings of the PCB multi-layer board, I found that this is another common old problem, but many designers do not understand the problems caused by the PCB factory!
First, let me talk about the problem I saw:
1. The distance between the BGA spherical centers is 0.4mm, and the design engineer designed the alignment between the BGA pads.
2. Design board vias between the four BGA pads.
Next, I will tell you why the PCB factory cannot produce such a design.
A: The BGA ball center distance is 0.4 mm and the BGA minimum is 0.2 mm, so the BGA pad spacing is only 0.2 mm.
If the lines are aligned, the minimum limit of the line is 3 mils, or 0.075 mm. In this way, only the distance between the wire and the pad is left:
(0.4-0.2-0.075) 2 = 0.0625 mm, only 2.46 mils. This distance is definitely not good!
Emphasis is placed on the two-point process of PCB production.
One: The minimum distance between the BGA clip and the pad is 3 mils, and the minimum distance between the BGA clip and the pad is 3 mils.
2. The final distance from the hole to any figure (line, pad, large copper plate):
Outer distance: 6mil. The limit distance inside the board: 8mil.
Some people may ask: Why is the internal spacing greater than the external requirements? Because, in the PCB production process, the deviation of the inner laminate alignment will be even greater!
At this point, the design engineer should be confused: Now there are more and more 0.2mm BGA chips, is there a way?
The answer is: must! With the advent of the smart age, electronic devices are becoming more and more complex, and these are issues that must be solved! Next, I will tell you the solution: design the holes in the board and take the resin plug hole technology!
The hole in the board, as the name suggests: the hole in the pad! So what kind of board manufacturing process is a loophole in the disk? I will introduce it in detail here!
The manufacturing process of the holes in the plate includes drilling, plating, resin plugging, baking and grinding. First, drill holes. The drill bit here is usually a laser hole.
The minimum limit of the mechanical hole is 0.15 mm. If the hole is 0.1mm, it must be drilled through the laser laser hole.
After drilling, the plated holes are metallized and then baked with a resin plug. Finally, the resin is ground into a flat shape. Since the polished resin does not contain copper, it must be changed to PAD again on the copper layer. These processes were completed prior to the original PCB drilling process, which means that the jacks were well handled before drilling other holes according to the original common PCB factory process. go.
Typically, as we mentioned, the perforated plate in the design pan will have blind or buried holes.
For example, one (PCB multi-layer) four-layer board: one layer - two layers perforated in the disc, then two layers - one layer out, then one layer - four layers can also be perforated.
Thus, a four-layer first-order HDI plate is formed: 1-2, 1-4 or 1-2, 1-4, 3-4.
Of course, the (PCB multi-layer board) 68-layer board can also use the same design, the first-order HDI circuit board of the conventional drill bit design shown in the following figure, for everyone to learn!