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Advantages of reverse-mount low-ohmic resistors

What is the current trend with low-ohmic resistors?

Besides exhibiting the correct resistance value, low-ohmic resistors that are compact but support high power and feature superior heat dissipation are increasingly required. To provide greater power handling capability and improved heat dissipation characteristics, products with larger chip sizes and units configured with wider electrodes are typically used.

Illustration : Larger size -> Increased power

Larger size → Increased power

Illustration : Wide terminal type -> Improved heat dissipation

Wide terminal type → Improved heat dissipation

However, increasing the chip size will require a larger mounting area, decreasing strength against temperature cycling.

Maintaining or improving power handling capability while decreasing chip size.

Wide terminal types can fit the need for higher rated power in a compact form factor.
However, although increasing the width of the terminal improves heat dissipation and rated power, one drawback is higher costs due to increased electrode material compared with conventional products.

  Advantages Disadvantages
Conventional High Power Type
  • Higher rated power
  • Reduced heat generation
  • Lower cost
  • Increased mounting area
  • Risk of solder cracking due to temperature cycling
Wide Terminal Type
  • Higher rated power
  • Improved heat dissipation
  • Higher material costs

To that point, as shown below, ROHM's UCR series provides an ideal balance between material costs and specifications.

Graph: Material Costs vs. Specifications (UCR Series)

Why does the UCR Series feature higher rated power than conventional types?

The UCR Series adopts a rear-mount configuration. This shortens the distance between the substrate and heat-generating elements, improving heat dissipation performance. In addition, materials and structure are optimized, ensuring higher rated power over conventional resistors and contributing to greater end-product miniaturization.

Illustration : Shorter thermal pathway improves heat dissipation characteristics
Rated Power Comparison
Size (mm) Top Mount Type
(Conventional
MCR Series)
Rear Mount Type
(UCR Series)
Wide Terminal Type
(LTR Series)
0603 0.05W 0.1W -
1005 0.063W 0.125W -
1608 0.1W 0.25W
(Partial 0.2W)
-
2012 0.25W 0.33W 0.5W
3216 0.25W 0.5W 1W

Adopting a rear-mount structure also minimizes the effects of additional resistance components from the top and sides of the electrodes, reducing resistance changes due to temperature (TCR).

Illustration : Not affected by additional resistance components from the top and sides of the electrodes.
Resistance Change Rate Comparison
Graph: Resistance Change Rate Comparison
Temperature Characteristics Comparison
Parameter Top Mount Type(MCR10) Rear Mount Type(UCR10)
Temperature Characteristics (ppm/℃) 500±300 0 to 250

Key Features

UCR Series (Rear-Mount Type)

Graph: Material Costs vs. Specifications (UCR Series)
  • Compact, high-power design
  • Superior temperature characteristics vs conventional top mount types
  • Lower material costs compared with wide terminal types

Lineup

Part No. Size
(mm)
Rated Power (at 70℃) Resistance
Tolerance
Temperature Coefficient
of Resistance (ppm/℃)
Resistance Range Operating Temperature
Range (℃)
Automotive
Grade (AEC-Q200)
UCR006NEW 0603 1/10W
(0.1W)
J (±5%) 0 to 300 100mΩ to 910mΩ
(E24 Series)
-55 to
+155
Pending
F (±1%)
UCR01 1005 1/8W
(0.125W)
J (±5%) 0 to 300
0 to 250
0 to 200
68mΩ to 91mΩ
(E24 Series)
100mΩ to 200mΩ
(E24 Series)
220mΩ to 910mΩ
(E24 Series)
YES
F (±1%)
UCR03 1608 1/4W
(0.25W)
J (±5%) 0 to 250
0 to 200
0 to 150
20mΩ to 47mΩ
(E24 Series)
51mΩ to 91mΩ
(E24 Series)
100mΩ to 200mΩ
(E24 Series)
YES
(100mΩ
and higher)
F (±1%)
1/5W
(0.2W)
J (±5%) 0 to 150
F (±1%)
UCR10 2012 1/3W
(0.33W)
J (±5%) 250±100
0 to 250
0 to 150
11mΩ to 15mΩ
(E24 Series)
20mΩ to 47mΩ
(E24 Series)
51mΩ to 100mΩ
(E24 Series)
YES
F (±1%) 0 to 250
0 to 150
11mΩ to 47mΩ
(E24 Series)
51mΩ to 100mΩ
(E24 Series)
UCR18 3216 1/2W
(0.5W)
J (±5%) 0 to 350
0 to 200
0 to 150
11mΩ to 18mΩ
(E24 Series)
20mΩ to 39mΩ
(E24 Series)
43mΩ to 100mΩ
(E24 Series)
YES
F (±1%)

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