1. Circuit board substrate design principles
First, DIE pads must be always the same direction with the bonding wire. And also
connection leads need to be the same direction with the pads .For each DIE, it must
place a criss-cross pads in the diagonal as alignment coordinate, which need to
connect the network. Generally choose ground (must have a network, otherwise the
cross will not appear).And in order to avoid the crucifix submerged by copper lead to
it couldn’t positioning accurate, normally prohibit laid copper box surround it. DIE
bound needs to remove no use pads that don’t require network connection. As shown
below.
Second, production process is special. Each line must be adopted by the plating line
plated brass casting techniques to format the pads and traces, or all other places need
to use copper. Here we must note that even if the pads with no electrical connection,
which don’t have a network, we must pull the copper pads out of the frame in eco
mode, and otherwise the pads will be no copper pads. Plating line pulled out the frame
need to identify the copper corrosion location in other layers. In general, the copper
beyond the frame inside 0.15mm, while the edge copper about 0.2mm distance from
the frame.

2. Third, it needs to determine positive and negative in the plate frame, the best to place
all parts the same side, and mark the side with XXX, as shown below:
Fourth, it is with the pads larger than normal and with special package for CX0201.
The difference of X identifies and C0201 is as follows:
0603 Pad: 1.02mmx0.92mm pad solder mask opening area: 0.9mmx0.8mm, two pads
center distance 1.5mm
0402 Pad: 0.62mmx0.62mm pad solder mask opening area: 0.5mmx0.5mm, two pads
center distance of 1.0mm
0201 Pad: 0.42mmx0.42mm pad solder mask opening area: 0.3mmx0.3mm, two pads
center distance of 0.55mm
Fifth, DIE requires minimum size of bonding pad (single line) 0.2mmx0.09mm 90
degrees, the minimum spacing between the pads 2mil, and the pad width of inner
rows of the ground and power lines 0.2mm.The angle of the bonding pad is adjusted
according to the angle of parts pulling line. It is not good for bonding wire too long in
the substrate. The minimum space between the main control DIE and inner layer
bound pad is 0.4mm, minimum space between FLASHDIE and bonding pad is 0.2mm.
The longest space of two wires should not exceed 3mm. Spacing between two rows of
pads should be separated by binding 0.27mm or more.

3. Sixth, the space between the SMT pads and DIE pad and SMT components should
keep above 0.3mm. Space between DIE pads also should be more than 0.2mm. Signal
traces minimum 2mil, pitch 2mil. The main power traces best to 6-8mil, try a large
area of copper pour. For the area couldn’t pour copper, consider power supply and
other signal lines to enhance the strength of the substrate.
Seventh, pay attention to the space between vias and pads, traces and gold finger
should be not too small. The via with same properties and gold finger should keep at
least 0.12mm above. The via with different properties should be far away from the
pad and gold fingers as possible. Minimum outside vias 0.35mm, inside vias 0.2mm.
Also pay attention to the copper shouldn’t be too close to gold finger when pour
copper. Some of the pieces copper need to delete, and avoid a large area with no
copper the same time.
Eighth, use grid when pour copper, the proportion 1:4. That is to say copper pour
0.1mm and 0.4mm laminate copper angle change 45 degrees.
Copper as shown: