Question 1

TDK's Guide to Electrically Conductive Adhesives (1): What is an electrically conductive adhesive?

Accepted Answer

A. It is a material that consists of an epoxy resin mixed with a conductive material, and is used to form conductive joints that connect electronic components to PCBs (Printed Circuit Boards). Due to its physical characteristics, electrically conductive adhesives are used as alternatives to the conventional SMT (Surface Mount Technology) in many applications. It is a material that frequently consists of an epoxy resin mixed with a conductive filler. Higher conductivity can be achieved by using more filler, however, this reduces the strength of the bond due to less adhesive material.
The conductive material contained in the epoxy is often silver (Ag), or, less frequently, a conductive form of carbon (e.g. graphite).

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Question 2

TDK's Guide to Electrically Conductive Adhesives (2): Why should I use conductive epoxy?

Accepted Answer

A. Conductive epoxies are mainly used in applications where the risks of mechanical and thermal cracking are very high, as well as when there are concerns about damaging heat sensitive components on the PCB during soldering.

Although tin/lead solders have been widely used for many years, leaded solders are becoming much less frequently used because of concerns over lead's toxicity. Unfortunately, unleaded solders have higher melting points, and because of this, sensitive electrical components near the solder joint can be damaged during the soldering process.

Another issue with lead-free solder is that it is less elastic than leaded solder. This means that lead-free solder joints will be more brittle and more susceptible to developing cracks than with lead-based solder, especially during temperature cycling.

Conductive epoxies are an alternative to leaded and unleaded solders. They have low curing temperatures, reducing the risk that heat sensitive components will be damaged during manufacturing, and they are more resilient to thermal and mechanical stress.

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Question 3

TDK's Guide to Electrically Conductive Adhesives (3): How does epoxy differ from solder during manufacturing?

Accepted Answer

A. The general process for mounting components with conductive epoxy is similar to solder mounting. The following table displays the differences.

Process	Epoxy	Solder
1	Disperse glue	Disperse solder
2	Place component	Place component
3	Cure	Heat/Reflow
4	Cool (if heated cure)	Cool

Table 1 : Epoxy and solder mounting processes.

The curing durations for epoxies are significantly longer than the heating and cooling times for solders, and care must be taken to make sure they are maintained at the proper temperature during curing, or the epoxy may not fully cure.

Conductive epoxies can be made in one or two part systems. One part systems have the advantage of not needing to mix the resins to form the final epoxy. They often have high curing temperatures (150°C), and often need to be refrigerated until used.

Two part epoxies have the advantage of being able to cure at lower temperatures (often room temperature) than single compound epoxies, plus they do not need to be refrigerated. These compounds need to be used immediately after mixing, and can be ruined by an improper mixing ratio of the curing agent.

Special care must be taken when placing the conductive epoxy. In the case of solder, excessive solder can be moved back to the landing point when heated because of the surface tension of the solder. However, epoxies cure without moving, and this can create shorts and silver migration issues (which could eventually result in a short).

Figure 1: Excessive solder and glue placement.

Figure 2: Short risk from excessive glue.

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Question 4

TDK's Guide to Electrically Conductive Adhesives (4): Does TDK offer MLCCs for use with conductive epoxy?

Accepted Answer

A. TDK offers many of our MLCC’s with a termination specifically designed for use with conductive adhesives. The termination for use with conductive epoxy uses an outer layer of an alloy consisting of silver (Ag), palladium (Pd), and copper (Cu) on top of a Cu layer. The standard termination of TDK’s MLCC’s consists of electroplated layers of nickel (Ni), and tin (Sn) on top of a copper layer.

Figure 1: MLCC termination for use with epoxy.

Figure 2: Standard MLCC termination.

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Question 5

TDK's Guide to Electrically Conductive Adhesives (5): Can I use an MLCC (Multilayer Ceramic Capacitor)  with a standard termination with conductive epoxy?

Accepted Answer

A. No. The termination used for epoxy mounting serves several purposes.

The addition of copper reduces the silver migration rate of the termination, which increases the amount of time it takes for a short to develop across the capacitor.

The conductive glue can absorb water, which would cause the Sn plating on a standard termination to oxidize. This increases the contact resistance between the MLCC and the conductive epoxy significantly (approximately 100 times greater after 100 hours), which leads to energy losses and heat generation. The AgPdCu alloy does not have the same oxidation issues as Cu/Ni/Sn and maintains a stable contact resistance.

Finally, during operation, temperature cycling can result in micro-cracks developing between the standard Cu/Ni/Sn termination and the epoxy, resulting in drastic reduction in shear force required to remove the chip from the board. The AgPdCu termination reduces the rate at which these micro-cracks develop because the silver contained in the termination and the conductive adhesive have a strong affinity for each other.

Figure 1: Contact resistance over time.

Figure 2: Shear force after temperature cycles.

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Question 6

TDK's Guide to Electrically Conductive Adhesives (6): What is the Difference Between “Soft Termination” and “Conductive Epoxy Termination”?

Accepted Answer

A. TDK's Soft Termination series is an MLCC with a layer of conductive resin built in to the standard termination.

The Conductive Epoxy series uses an AgPdCu termination for use with conductive epoxy as a mounting adhesive (solder replacement).

Both series allow for greater resistance to cracking due to mechanical stress, and significantly more resistance to cracking due to thermal shock. Additionally, the low curing temperatures of the conductive epoxy series preserve heat sensitive components during manufacturing.

Figure 1: MLCC with soft termination.

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Question 7

TDK's Guide to Electrically Conductive Adhesives (7): What type of epoxy should I use?

Accepted Answer

A. Because epoxy technology is so mature, many companies can engineer a variety of compounds for an even greater variety of specifications. Conductive epoxies can be modified and manufactured to meet many different performance characteristics and specifications including cohesive strength, hardness, durability, flexibility, temperature resistance, viscosity, thermal conductivity, electrical conductivity, moisture resistance, chemical resistance, resistance to mechanical shock and vibration, as well as the ability to withstand ultra-high or cryogenic temperatures.

As with all engineering, there are trade-offs for every type of epoxy. For example, epoxies with higher conductivity have a weaker bond strength because of the greater filler to resin ratio. Thorough research of the advantages and disadvantages of each type of epoxy should be conducted in order to ensure the epoxy will meet the required specifications.

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Question 8

Terminal Adhesion (1): What can cause MLCC (Multilayer Ceramic Chip Capacitor) to come off the printed circuit board (PCB) after soldering?

Accepted Answer

A. Any number of things can cause this problem, however the most common are solder joint quality and harsh handing. Solder joint quality here means the solder fillet volume and its coverage on the component’s termination.

Figure 1: Side view of soldered component

The adhesion between the component and the PCB is directly proportional to the amount of solder used in most cases.

Solder fillets typically become smaller as the component becomes smaller, and the lack of solder mass will reduce the adhesion strength also.

Figure 2: Terminal adhesion increases with solder amount

Figure 3: Solder amount increases with case size increase

Abusive handling obviously can cause the capacitors to come off after soldering, but even normal handling can dislodge a component from the PCB with small solder fillets. Touching the populated PCB with the hand or instrument should be a point of training and minimized as much as possible. Also, aqueous washes offer use higher water pressure than necessary when cleaning flux from the board. Brushes, conveyors, and robotics are all areas of handling risk.

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Question 9

Terminal Adhesion (2): What is “terminal adhesion” of MLCCs (Multilayer Ceramic Chip Capacitors)?

Accepted Answer

A. Terminal adhesion is the amount of force required to remove a component's termination from its body. It is most often evaluated by an axial lead pull or side push test. It is typically expressed in kilograms and is dependent upon component case size.

Figure 1: Traditional terminal adhesion tests

The axial lead pull is the best measure of a component’s true terminal strength, but the side push method takes into consideration the SMT process as a whole.

Note: The side push method is heavily dependent upon solder amount and the push point on the component.

The magnitude of terminal adhesion should always be discussed together with the failure mode. The three basic modes of failure are illustrated below.

Figure 2: Failure modes, lead pull

Figure 3: Failure modes, side push

The failure mode can change with varied solder fillet heights. A ceramic-to-ceramic or metal-to-metal failure mode typically yields the highest strengths and is therefore generally preferred.

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Question 10

Terminal Adhesion (3): What is the proper amount of solder when using an MLCC (Multilayer Ceramic Capacitor)?

Accepted Answer

A. The solder fillet is most practically expressed in terms of coverage of the component’s height or thickness.

TDK recommends the solder fillet to be 50% of the MLCC thickness. Additionally a thin layer of solder typically extends beyond the fillet’s bulbous volume, indicating the termination was properly “wet” by the solder and therefore exhibits good solderability. EIA*1 recommends >25% of the component thickness.

Note: Often manufactures will try to minimize the amount of solder used for cost control or tombstone prevention, however great care must be used to avoid sacrificing adequate solder fillets and proper terminal adhesion.

Figure 1: Solder fillet*2

*1 ANSI/J-STD-001B, Oct 1996
*2 TDK Multilayer Ceramic Chip Capacitors. Application Manual, Sept 1988 (publication BBE-017A).

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Question 11

Terminal Adhesion (4): What MLCC (Multilayer Ceramic Capacitor) variables effect terminal adhesion?

Accepted Answer

A. Solderability and plating thickness4 play an important role in terminal adhesion, however it is the MLCCs material system that is most significant.

Figure 1: MLCC inner structure

The material system used in a ceramic capacitor is rather complex, especially when considering the bond between the ceramic dielectric and the metal electrodes. The type and amount of glass frit used in the termination paste as well as the ceramic dielectric formulation are key variables for terminal adhesion. The co-firing temperature profile and atmosphere provide the catalyst for the termination-ceramic bond to occur.

Figure 2: Glass frit penetrates the ceramic dielectric

* C.F.Smith, Jr., “End Termination Compositions for Multilayer Chip Capacitor: Platable Bases and Plating”, 37th Electronics Components Conference, 1986.

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Question 12

Terminal Adhesion (5): What should I do to ensure good terminal adhesion?

Accepted Answer

A. By far the most common problem associated with poor terminal adhesion is too small of a solder fillet. Properly sized stencil apertures and a printing process free of "blinding" are crucial. Avoiding too fast of a solder profile will help ensure good solder flow and provide proper solder coverage.

Contaminated solder lands could effect the adhesion between the solder fillet and the PCB. Only clean PCBs (free of oils, moisture-free, etc.) should be used to ensure good terminal adhesion.

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Question 13

Commentary video of flex crack countermeasures for MLCCs (Multilayer Ceramic Capacitors)

Accepted Answer

﻿	&#13;&#13;<div class="grayBorderBox01 b20">&#13;<p class="t0 b10 indent02 fontRed02 text18" style="display:none;"><span class="fontRed">Q.</span>Commentary video of flex crack countermeasures for MLCCs (Multilayer Ceramic Capacitors) <drupal-entity data-align="" data-caption="" data-embed-button="acquia_dam" data-entity-embed-display="media_image" data-entity-embed-display-settings="{"image_style":""&#44"image_link":""}" data-entity-type="media" data-entity-uuid="71944a58-a9ed-4808-80a0-1dd49a7409f8" data-langcode="ja" alt="" title="" class="" style="" id-img="" usemap=""></drupal-entity></p>&#13;<p class="t0 b10 pad03 glay01 text11" style="display:none;">&#13;Capacitors > &#13;Ceramic Capacitors > &#13;Multilayer Ceramic Chip Capacitors</p>&#13;<p class="t0 indentQA"><span class="fontBlue text18">A.</span>&#13;</p><div class="centerBox">&#13;&#13;&#13;<div style="display:none">&#13;&#13;</div>&#13;&#13;&#13;&#13;<script language="JavaScript" type="text/javascript" src="https://sadmin.brightcove.co.jp/js/BrightcoveExperiences.js"></script><object id="myExperience912523362002" class="BrightcoveExperience">&#13;  <param name="bgcolor" value="#FFFFFF" /><param name="width" value="486" /><param name="height" value="412" /><param name="playerID" value="577678871002" /><param name="playerKey" value="AQ~~&#44AAAAhoBQ6aI~&#44Wyi3gLMBrgcLnExVPa9UwokUocWF06EL" /><param name="isVid" value="true" /><param name="dynamicStreaming" value="true" /><param name="@videoPlayer" value="912523362002" /><param name="secureConnections" value="true" /><param name="secureHTMLConnections" value="true" /></object>&#13;&#13;&#13;<script type="text/javascript"><![CDATA[// ><!]]></script></div>&#13;&#13;&#13;&#13;</div>

Question 14

Since it seems that inductors for high frequency circuits uses dielectric ceramics as the their material&#44 I am concerned about magnetic flux leaking out.

Accepted Answer

A. Leakage of magnetic flux from an inductor may impact adjacent parts or peripheral circuits.
For this reason, please check the level of impact through experimental evaluation, etc.
In order to reduce the impact of magnetic flux leakage, countermeasures such as widening the distance between products or mounting them can be taken.
TDK's multilayer inductors for high frequency circuits (excluding the MLK series [Gigaspira structure]) have direction identification markings, which enable identification of the direction of magnetic flux.

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Question 15

What is a "magnetic shield type" power inductor (inductor for power circuits)?

Accepted Answer

A. The exterior of the product is covered with magnetic material. This prevents magnetic flux leakage inside the product from leaking outside. It also makes the product more resistance to external influences.
As information on shields for power inductors, TDK has published the “Selection Guide for Power Inductors in Consideration of Leakage Flux.”

Characteristics of each shield type

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Question 16

Does singing become an issue with inductors&#44 as in the case of multilayer ceramic capacitors? If so&#44 what countermeasures can be taken?

Accepted Answer

A. When a current in the audio frequency range is applied to an inductor, singing may occur due to the magnetostrictive property of the magnetic material or attraction between components such as core and wires.
The most effective countermeasure is not applying currents in the audio frequency range.
If application of current in the audio frequency range is inevitable, modifying the product shape or switching to another type may change the natural frequency of the entire circuit, including the substrate, and reduce singing.
As material on singing, TDC has published the “Solutions for Silencing DC-DC Converters—Measures Against Acoustic Noise in Power Inductors.”
For other questions, please send inquiries to your nearby sales office or distributor, or send inquiries from this website.

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Question 17

What are the coils for decoupling?

Accepted Answer

A. A coil for decoupling is series-connected to the power circuit and has two major functions.

1. Suppression of high frequency noise
In the coil, the higher the frequency of the alternating current, the more resistance it encounters. This means that high frequency noise is reflected and blocked. An LC filter (low-pass filter), which is a coil combined with a capacitor, is often used to improve efficiency.
Unlike the coil, in the case of the capacitor, the higher the frequency, the more easily the current passes. High frequency noise reflected by the coil, therefore, travels through the capacitor and is bypassed to the earth side.
2. Stabilization of the power supply voltage
When there are fluctuations in the current, the coil emits an electromotive force in a direction that stops the fluctuation (the coil's self-induction function), and stores the electric energy as magnetic energy. The coil then emits the stored magnetic energy to regulate the power supply to the IC whenever there are momentary surges of power.

TDK offers wire-wound and multilayer types of coils for decoupling, in commercial grade and automotive grade.

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Question 18

Can they be washed?

Accepted Answer

A. Yes, they can be washed. The conditions recommended by TDK are as shown below.

Cleaning solution	Isopropyl alcohol
Condition	Ultrasonic cleaning

[20W/l or below at 28kHz to 40kHz for 5 min or less at room temperature]

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Question 19

Do chip beads make squeaking noises like multilayer ceramic capacitors? What should be done if any squeaking noises are produced?

Accepted Answer

A. They may produce squeaking noises due to the magnetostrictive properties of magnetic materials. However, these squeaking noises are generally found only at high currents and the possibility of chip beads with low rated currents producing these sounds is low.

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Question 20

Can common mode filters / chokes be washed?

Accepted Answer

A. The MPZ series and the HF series products require ultrasonic cleaning [20W/l or less, 28kHz to 40kHz, 5 minutes or less at a room temperature]
The ACM series products can be washed by ultrasonic cleaning using isopropyl alcohol (IPA) or pure water for several tens of seconds.
Please be reminded that, since the ACM series products have exposed wires, applying a strong ultrasonic wave or cleaning for a long period of time may cause wire breakage.

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Question 21

Are there any restrictions for wire wound type common mode filters / chokes when a gold foil pattern is used on the circuit board to which they are mounted?

Accepted Answer

A. If the connection part of the wire is on the side of the circuit board, disconnection due to "solder erosion" may occur.
If the connection part is on the opposite side of the circuit board, there is likely almost no risk caused by "solder erosion."

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Question 22

Can I apply coating for moisture prevention on common mode filters / chokes?

Accepted Answer

A. The impact of a moisture proof material on the products depends on the type, application method, application amount, or application location of the material; therefore, we cannot guarantee the performance of our products.
Please test moisture proof agents on the actual products and independently manage them.

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Question 23

How can I know the composition of the electrodes or terminals?

Accepted Answer

A. Please specify the relevant product and please contact our sales representative or distributor, or contact us through this web site

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Question 24

Can I apply resin on common mode filters / chokes?

Accepted Answer

A. In general, they do not support resin application. However, since some resins may be supported, please specify the relevant product and please contact our sales representative or distributor, or contact us through this web site.

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Question 25

What types of TDK Thermistors are there?

Accepted Answer

A. There are NTC elements such as surface mount device (SMD) chip types, glass seal types, and resin coating types as well as NTC sensor assemblies/systems that meet the various installation and usage requirements.

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Question 26

If condensation occurs&#44 would this result in poor accuracy in any way?

Accepted Answer

A. Possible causes of deterioration if condensation occurs is the tainting or melting of the polymeric membrane, and if there are any impurities in the dew condensation, they can react to the ions and cause deterioration.
There is only a small possibility of any major property deterioration with condensation occurring once or twice, but the possibility of deterioration increases with the number of times condensation occurs. Please use the product after checking your usage environment.

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Question 27

Are humidity sensors CHS-UGS affected by atmospheric pressure?

Accepted Answer

A. Polymeric type humidity sensors are used for our humidity sensors so basically they should not be affected much by atmospheric pressure.

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Question 28

Are there any recommended conditions for when using magnets in sets?

Accepted Answer

A. Using cylindrical NdFeB (isotropic) magnets with a size of Φ13-20㎜ and thickness of 2-3㎜ is recommended. Magnets for sensors can also be provided.

Question 29

Please describe the positional relationship between magnets and sensors.

Accepted Answer

A. Automotive applications include their use in position sensing for motors such as EPS motors and those for various actuators, wipers, and position sensing for steering angle sensors.
Their applications in industrial equipment are for when precision is required such as with motor actuators, flowmeters, and measuring instruments.

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Question 30

Which kind of contacting technology can be used?

Accepted Answer

A. The contacting technology depends on the used disk metallization. The disk metallization is in general suitable for gluing, iron soldering, reflow soldering, clamping or welding applications. For some disk metallization gluing is preferred, these types have a remark in the data sheet field features.

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