DATA SHEET
CHIP RESISTORS
Mounting
Product Specification – February 13, 2018 V.10
Feb. 13, 2018 V.10
www.yageo.com
Mounting
Product specification
Chip Resistor Surface Mount
2
8
MOUNTING
Due to their rectangular shape and small dimensional
tolerances, Surface Mounted Resistors are suitable
for handling by automatic placement systems. Chip
placement can be on ceramic substrates and printed-
circuit boards (PCBs). Electrical connection to the
circuit is by wave, vapour phase or infrared
soldering. The end terminations guarantee a reliable
contact and the protective coating enables ‘face
down’ mounting.
The laws of heat conduction, convection and
radiation determine the temperature rise in a
resistor owing to power dissipation. The maximum
body temperature usually occurs in the middle of the
resistor and is called the hot-spot temperature.
The hot-spot temperature depends on the ambient
temperature and the dissipated power. This is
described in the data sheets under the chapter
heading “Functional description”.
The hot-spot temperature is important for mounting
because the connections to the chip resistors will
reach a temperature close to the hot-spot
temperature. Heat conducted by the connections
must not reach the melting point of the solder at the
joints. Therefore a maximum solder joint
temperature of 110 °C is advised.
The ambient temperature on large or very dense
printed-circuit boards (PCBs) is influenced by the
dissipated power. The ambient temperature will
again influence the hot-spot temperature. Therefore,
the packing density that is allowed on the PCB is
influenced by the dissipated power.
E
E
X
X
A
A
M
M
P
P
L
L
E
E
O
O
F
F
M
M
O
O
U
U
N
N
T
T
I
I
N
N
G
G
E
E
F
F
F
F
E
E
C
C
T
T
S
S
Assume that the maximum temperature of a PCB is
95 °C and the ambient temperature is 50 °C. In this
case the maximum temperature rise that may be
allowed is 45 °C.
In the graph (see Fig.1), this point is found by
drawing the line from point A (PCB = 95 °C) to
point B (T
amb
= 50 °C) and from here to the left axis.
To find the maximum packing density, this horizontal
line is extended until it intersects with the curve,
0.125 W (point C). The maximum packing density, 19
units/50 × 50 mm2 (point D), is found on the
horizontal axis
Fig. 1 PCB temperature as a function of applied power, mounting density and ambient temperature
The laws of heat conduction,
convection and radiation determine the
temperature rise in a resistor due to
power dissipation.