Tom
12-05-2002, 04:59 PM
IPC Advanced Study Guide Page Reference: Page 216 & 217, Section 4.6
Location of the via to Vcc can also be of importance. In a non-preferred condition, for either digital or RF, the distance that the via is from the land can be important. A distance greater than 3.5 mm is almost always too long a route in order to be effective.
The two most important issues: the lower value (picofarad) should be the closest to the pin. The micofarad capacitor can be further away if needed. These two are connected in parallel between the pin and ground. The relationship between the location of the via (V), Capacitor, (C), and the Pin (P) is such that a VCP condition is preferred; a CVP is acceptable; and a CPV is not preferred.
Also, don’t overlap a digital voltage over an analog ground. A technique for handling that condition is to split the plane into the two ground returns and position the circuitry over their respective planes.
Heat dissipation considerations include the use of large conductor planes to thermally manage the heat developed by high thermal radiating parts. The conductor planes can act as a heatsink for dissipating the component heat to other parts of the board or enclosure. Thus both voltage and ground planes serve a dual purpose.
The below picture is not preferred for RF or Digital circuits.....
Location of the via to Vcc can also be of importance. In a non-preferred condition, for either digital or RF, the distance that the via is from the land can be important. A distance greater than 3.5 mm is almost always too long a route in order to be effective.
The two most important issues: the lower value (picofarad) should be the closest to the pin. The micofarad capacitor can be further away if needed. These two are connected in parallel between the pin and ground. The relationship between the location of the via (V), Capacitor, (C), and the Pin (P) is such that a VCP condition is preferred; a CVP is acceptable; and a CPV is not preferred.
Also, don’t overlap a digital voltage over an analog ground. A technique for handling that condition is to split the plane into the two ground returns and position the circuitry over their respective planes.
Heat dissipation considerations include the use of large conductor planes to thermally manage the heat developed by high thermal radiating parts. The conductor planes can act as a heatsink for dissipating the component heat to other parts of the board or enclosure. Thus both voltage and ground planes serve a dual purpose.
The below picture is not preferred for RF or Digital circuits.....