Integration of passive components in circuit boards or modules

The technical requirements for complex electronic circuits are ever increasing, while the form factor is constantly being reduced. The integrated circuits use the space above circuit boards, and passive components – particularly block capacitors – need to be as close as possible to the CPU. The solution is to integrate passive components under the CPU or directly into the circuit board.

In future, circuit board manufacturers are going to need to focus more on the mounting of electronic components in order to be able to offer highly integrated solutions.

Circuit board manufacturers have already integrated antennas, resistors and capacitors in their circuit boards in the past via the conductor traces and the surface areas of the traces. However, particularly when it comes to capacitors, circuit board manufacturers soon reach the limits in terms of the available magnitude of capacitance, which is only around 4 on FR4 circuit boards. On ceramic capacitors, the permittivity is higher than 10,000, depending on the type of ceramic used.

The market needs electronic components that are easy to integrate in the circuit board production process.

The requirements of circuit board and module manufacturers can be summarised as follows:

• Minimal component heights
• Minimal tolerances in the Z direction
• Copper or gold outer electrodes
• Advantageous electrode form
• Maximised electrical performance
• Mechanical stability

Available components: Embedded passive devices (EPD)

Resistors:

The integration of resistors in resistors is not a new development in resistor networks, and the implementation of ever-smaller designs down to 008005 has also been completed. However, marketable designs with smallest component heights are required for integration. Here, KOA offers the series XR73 in the basic designs 0201 and 0402 with a component height of just 0.13 ± 0.02 and 0.14 ± 0.03 mm respectively. The embedded resistors cover a range of values from 1R to around 10MR in accordance with E96 1 % or E24 5 %. The copper outer electrodes have larger contact surface areas in comparison to standard resistors of the same size and design.

Multilayer ceramic capacitors (MLCC):

As the name already indicates, MLCC capacitors consist of alternating layers of metallised ceramic plates that are connected to the outer electrodes. In order to increase the capacitance with the same component footprint and using the same ceramic materials, multilayer ceramic capacitors have been made taller ever since they were first invented.

However, some manufacturers are able to offer the same capacitance with so-called low profile capacitors. The technical background is the availability and processing of smaller grain sizes of the ceramic material.

 

Cross-section of an MLCC at the connection side

Component size 0402 [1.0 x 0.5 mm]
Overall thickness 100 µm
Thickness of nickel layer 1 µm
Thickness of outer electrode layer, copper layer 10 µm

Picture source: Taiyo Yuden

The current product range from Taiyo Yuden for embedded ceramic capacitors with copper outer electrodes covers the following values in the sizes 0402 & 0201:

The lowest profile component currently available is offered in the size EIA0201 [0.6 x 0.3 mm] with a component height of 0.08 mm (tin outer electrodes). This component is specified with a rated voltage of 2.5 V, a nominal capacitance of 100 nF and an X5R ceramic capacitor.

The relatively new size 008004 [0.25 x 0.125 mm] with a thickness of 0.125 mm currently permits capacitances in the range from 220 pF to ~22 nF for X5R and 0.2 pF to ~8.5 pF for C0G with a tiny component footprint.

Inductors

SMD type inductors are available both in wire-wound and multilayer technology. The core materials can consist of ceramics, ferrite or also metal composites.

Low profile designs include e.g.:

Wire-wound – CBMF series:

0603 [1.6 x 1.8 mm] component height 0.8 ± 0.2 mm; value range 1 µH to ~47 µH for e.g. IS: 0.29 A IT: 0.77 A @ L: 1 µH

Multilayer – CKP series:

0603 [1.6 x 1.8 mm] max. component height 0.95 mm; value range 0.33 µH to ~2.2 µH for e.g. I: 0.75 A @ L: 1 µH

1008 [2.5 x 2.0 mm] max. component height 1.00 mm; value range 1 µH to ~2.2 µH at e.g. I: 1.2 A @ L: 1 µH

Multilayer high-frequency – HK series:

0201 [0.6 x 0.3 mm] component height 0.3 ± 0.03 mm; value range 1 nH to ~100 nH

Power metal composite – MC series:

0603 [1.6 x 1.8 mm] max. component height 0.6 mm; value range 0.24 µH to ~1 µH for e.g. IS: 2.0 A IT: 1.3 A @ L: 1 µH

SMD ferrite bead – BK/BKP series:

01005 [0.4 x 0.2 mm] component height 0.2 ± 0.02 mm

Advantages of EPDs at a glance

• Increased integration of circuit design, approx. 30-60 % of a conventional design
• Shorter paths, reduced losses
• Very good high-frequency response
• Better heat dissipation in the PCB than via conductor traces, heat radiation and air convection
• Lower interference emissions – EMC!
• Increased reliability
• Improved response to fast temperature change cycles
• Epoxy resin prevents corrosion due to O2 and H2S corrosive gases

Aspects of EPDs to be discussed

• Shelf life of embedded passive devices
• Oxidation of the copper electrode
• Resistance to acids and alkaline solutions
• Laser processability
• Mechanical stress
• ESD compatibility
• Lack of cross-manufacturer standardisation to date

Please get in touch if you have further technical questions or wish to order free samples.