General profile
The buried via is the hole made between inner layers used to interconnect the inner layer signal. It can not be visible from surface layers of top and bottom layer. Generally, they're often used on the mobile phone,PDA board etc.
Advantages
A) Reduce the probability of signal interference;
B) Keep the continuity of the characteristic impedance of the transmission line;
C) Save wiring space, suitable for high density and high speed circuit board design;
Application
Mobile phone, PDA boards, telecommunications, complext modules.
Design For Manufacture
This manufacturability guide provides an overview of various areas that printed circuit board designer may take into consideration on the fabrication possibility, manufacturing cost and reliability of their products. This DFM is divided into 6 parts for our readers. This is the section I.
| Serial NO. |
Procedure |
Item |
Manufacturing capability |
| Large volume (S<100 m²) |
Middle volume (S<10 m²) |
Prototype(S<1m²) |
|
| 1 |
Inner layer (18um, 35um, 70um etc are finished copper. If not mentioned copper, finished 1oz is the default value ) |
Min.isolation of layers |
0.1mm |
0.1mm |
0.06mm |
| 2 |
Min.track and spacing |
5/5mil(18um) |
4/4mil(18um) |
3/3.5mil(18um) |
| 3 |
5/5mil(35um) |
4/4mil(35um) |
3/4mil(35um) |
| 4 |
7/9mil(70um) |
6/8mil(70um) |
6/7mil(70um) |
| 5 |
9/11mil(105um) |
8/10mil(105um) |
8/9mil(105um) |
| 6 |
13/13mil(140um) |
12/12mil(140um) |
12/11mil(140um) |
| 7 |
Min.distance from drill to conductor |
4 Layer 10mil,6 layer 10mil,8-12 layer 12mil |
4 layer 8mil,6 layer 8mil,8-12 layer 10mil,14-20 layer 14mil,22-32 layer 18mil |
4 layer 6mil,6 layer 6mil,8-14 layer 8mil,16-22 layer 12mil,24-32 layer 14mil |
| 8 |
Min.width of annular ring on inner layer |
4 Layer 10mil(35um),≥6 Layer 14mil(35um) |
4 Layer 8mil(35um),≥6 layer 12mil(35um) |
4 Layer 6mil(35um),≥6 Layer 10mil(35um) |
| 9 |
Inner layer isolation ring width(Min) |
10mil (35um) |
8mil (35um) |
6mil (35um) |
| 10 |
Min.via pad diameter |
20mil (35um) |
16mil (35um) |
16mil (35um) |
| 11 |
Min. distance from board edge to conductor(no copper exposured)(inner layer) |
14 mil(35um) |
12 mil(35um)) |
8 mil(35um) |
| 12 |
Maximum copper weight(Inner layer and outer layer) |
3 OZ( 105 um ) |
4 OZ ( 140 um ) |
6 OZ( 210 um ) |
| 13 |
Core with different copper foil on both sides |
/ |
18/35,35/70 um |
18/35,35/70 um |
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