Unlike metals and hard resins, adhesive materials are easily affected by time and temperature.

When temperature rises while a constant force is applied, the adhesive layer can deform over time.

Even if each layer’s position is aligned immediately after processing, positions may change little by little due to

・High-temperature storage

・Long-term use

・Tightening of the reel winding

・Temperature cycles

・The weight of components and fastening loads

What becomes a problem here is not only the case where the entire component moves greatly.

For example, the heat dissipation layer shifts 0.2 mm relative to the heat source.

Conductive material is slightly exposed from the edge of the insulating film.

The position of the peeling tab changes, making it harder for the automated machine to grip.

Even such small changes become major problems in fine components and high-density mounting.

Therefore, positional accuracy must be evaluated not only at the position immediately after lamination,

but all the way to the position after temperature and time have passed.

Products do not heat up just once.

When the power is turned on, they generate heat.

When the power is turned off, they cool.

In automotive equipment, the outside temperature also changes greatly.

In servers, temperature fluctuates with computing load.

Through this repeated heating and cooling, dissimilar materials expand and contract again and again.

Even if one temperature change causes no problem, repetition may cause

・Fatigue of the adhesive interface

・Progression of edge peeling

・Minute gaps becoming larger

・Cracks in hard materials

・Warping that no longer returns

What is required of thermal management components is not only initial adhesion.

It is maintaining the same contact state even through repeated temperature changes.

Resin films, foams, adhesive materials, and so on can absorb moisture.

Moisture absorption can change

・Dimensions

・Hardness

・Adhesive strength

・Electrical insulation

・Flatness

Even if metal foil itself changes little with moisture, if only the resin film laminated with it stretches, the laminate warps.

If the humidity differs between the processing environment and the customer’s factory, dimensions that matched during processing may change during use.

For example, materials are placed in different environments, such as

・A dry processing room

・A high-humidity transport environment

・An air-conditioned customer factory

・A high-temperature, high-humidity product interior

That is why dimensional accuracy must be thought of not as accuracy at the moment it comes out of the processing machine,

but as accuracy maintained in actual storage, transport, and usage environments.

Automated supply tends to be thought of as the process of lining up components on a reel and applying them with a robot.

In reality, however, multiple operations are performed in succession:

1.Stably feeding out the reel

2.Recognizing the component position

3.Peeling from the carrier

4.Picking up with a nozzle

5.Transporting while maintaining posture

6.Applying in the correct position

7.Compression bonding with the necessary pressure

If even one of these is unstable, the process stops.

For example, problems occur such as

・The component is warped and cannot be picked up

・Narrow parts stretch during peeling

・Reel pitch changes

・The adhesive surface sticks to the nozzle

・The component rotates during transport

・It makes contact from the edge during application and air bubbles get in

In other words, a component suited to automation is not a component that an automated machine can hold.

It is a component that moves the same way every time, from peeling to application.

In reel-to-reel processing, tension is applied to transport materials stably.

If tension is too weak,

・The material sags

・It meanders

・The processing position is unstable

・Wrinkles occur

may result.

On the other hand, if tension is too strong,

・Resin films stretch

・Thin metal foil deforms

・Foams become narrower

・Component pitch changes

・Warping occurs after lamination

may result.

The problem is that if dimensions and pitch are set while the material is stretched during processing, the material springs back after the tension is released.

Even if the pitch is 100 mm on the processing machine, it may change if tension conditions change after winding or in the customer’s equipment.

Therefore, in reel processing, it is necessary to consider everything from

・Tension of the raw material

・Tension during lamination

・Tension during die-cutting

・Tension during winding

・Feed tension in the customer’s equipment

When laminating dissimilar materials in reel form, separate tension is applied to each material.

For example, suppose they are laminated while only the upper film is pulled strongly.

Immediately after lamination, the position looks aligned on the camera.

However, when the tension is released after winding, the upper film tries to return to its original length.

As a result,

・The laminate warps

・The positions of the layers shift

・Component pitch changes

・Edges lift

・The reel meanders

may result.

In high-precision lamination, looking only at alignment is not enough.

What matters is the tension state under which the position was aligned.

Even if components can be wound into a reel, that does not necessarily mean they are suited to automated supply.

Components wound on a reel are subjected to

・Bending

・Compression

・Tension

・Long-term constraint

Especially at the start of winding, the winding diameter is small and large bending is applied to the component.

Hard laminated materials.

Thick foams.

Brittle graphite.

Multilayer composite components.

Winding may cause these to develop

・Curl from winding

・Edge lifting

・Interlayer delamination

・Cracks in graphite

・Adhesive squeeze-out

What matters is not whether it can be wound.

It is whether it returns to the necessary flatness after being wound.

If the reel core diameter is small, equipment and packaging can be made smaller.

However, the bending applied to the component becomes larger.

Making the core diameter larger can reduce curl from winding.

On the other hand,

・The entire reel becomes larger

・It may not fit in the equipment

・Transport and replacement may become difficult

・Storage space may increase

Therefore, core diameter is not merely a packaging specification.

It must be decided from

・Component thickness

・Bending stiffness

・Brittleness

・Curl from winding

・The customer’s equipment

・Supply quantity

The reel diameter is also part of the processing design for maintaining component performance.

When a reel is wound, pressure from the outer material is applied to the inner material.

The stronger the winding tension, the greater the pressure applied to the inner layers may be.

Soft adhesive materials, foams, gel-like TIM, and so on may, due to this pressure,

・Decrease in thickness

・Squeeze out from the edges

・Adhere strongly to the carrier

・Increase in peeling force

・Deform in outer shape

Even if it is normal immediately after processing, it may become hard to peel after being stored in reel form for several weeks.

Therefore, for reel products, it is necessary to check the state

・Immediately after processing

・Immediately after winding

・After a certain period of storage

・After transport vibration

Even within one reel, the conditions the component is subjected to differ between the start of winding, the middle, and the end of winding.

The start of winding may have

・A small bending radius

・Long-term pressure

・A large effect from winding tightness

The end of winding may

・Have a large bending radius

・Be more susceptible to external impact

・Be more susceptible to winding misalignment and loosening

That is why judging quality by sampling only one place from a reel may not be enough.

At least at

・The start of winding

・The middle

・The end of winding

the approach of checking

・Peeling force

・Pitch

・Warping

・Appearance

・Thickness

is necessary.

When an automated machine uses a component, in many cases it peels the component from the release film.

At this point, force in the peeling direction is applied to the component.

In particular,

・Thin films

・Soft TIM

・Long, narrow components

・Graphite

・Complex irregular shapes

・Components with a large adhesive area

tend to deform during peeling.

If peeling force is too high,

・The component may stretch

・The edges may bend

・Narrow parts may tear

・The stacking position may shift

・Graphite may crack

On the other hand, if peeling force is too low,

・The component may lift during transport

・Its position may shift on the reel

・Double picking may occur

・The product may also be lifted during scrap removal

What is needed is not simply that it peels off.

It is that it can be peeled with the same force every time without changing its shape.

The peelability of a component is not determined only by the combination of materials.

It changes with

・Peeling angle

・Peeling speed

・Temperature

・Carrier hardness

・Adhesive area

・Surface condition of the release film

A component that could be peeled by hand at low speed may not peel on a high-speed automated machine.

Conversely, peeling suddenly at high speed can deform soft components.

In addition, methods that peel components by sharply folding back the carrier make peeling easier, but may apply large bending to brittle materials.

Therefore, peeling evaluation must be done at angles and speeds close to the actual equipment.

Even for components with the same outer shape, how easily they deform changes depending on where peeling starts.

Peeling from a wide side.

Peeling from a narrow tip.

Peeling from a sharp corner.

These apply different forces to the component.

If peeling starts from a narrow protrusion or sharp corner, stress concentrates, and the component may

・Stretch

・Fold

・Tear

・Delaminate between layers

That is why, in shapes for automation, measures are needed such as

・Arranging components in an orientation that is easy to peel

・Not placing narrow parts on the peeling start side

・Providing peeling tabs as necessary

・Supporting components on the carrier

Even parts that are unnecessary in the finished product may be necessary to stabilize the volume production process.

A person can hold a slightly warped component while pressing it with their fingers.

An automated machine lowers its nozzle to a set position and picks up the component with vacuum.

If the component is warped,

・A gap forms with the nozzle

・Vacuum leaks

・It cannot be picked up

・It shifts the moment it is lifted

・It falls during transport

may result.

Thermal management components in particular include ones that

・Have many holes

・Are narrow

・Have rough surfaces

・Are porous

・Are soft

・Have exposed adhesive surfaces

That is why shapes for automation must secure

・An area the nozzle can contact

・Suction positions that avoid holes

・A flat suction surface

・A position close to the component’s center of gravity

・A surface through which vacuum is unlikely to leak

Foams, gels, flexible thermally conductive sheets, and so on can deform when lifted with a vacuum nozzle.

Only the nozzle area lifts.

The surroundings sag.

Narrow parts fold.

Adhesive surfaces touch each other.

It sways during transport and its position changes.

Countermeasures to such problems may include

・Increasing the suction area

・Supporting with multiple nozzles

・Providing a temporary reinforcing film

・Transporting together with the carrier

・Providing support parts for the process

What matters here is that the shape needed as a finished product and

the structure needed to maintain the shape during transport are not necessarily the same.

In complex irregular-shaped components, the center of the outer shape and the center of gravity of the component may not coincide.

For example, copper foil is laminated on only one part.

A thick foam is provided on only one side.

Adhesive material is placed on only one part.

In such components, weight is biased to one side.

Even if the center of the outer shape is picked up, the component may tilt or rotate during transport.

Therefore, the suction position must be considered not as the center on the drawing,

but as the center for transport, including the component’s weight and stiffness.

Automatic application equipment sometimes uses cameras to recognize the position and orientation of components.

However, many thermal management components are made of materials that are difficult for image recognition.

For example,

・Black graphite

・Glossy copper foil and aluminum foil

・Transparent insulating film

・Left-right symmetrical outer shapes

・Thin materials with outlines that are hard to see

With left-right symmetrical components, the orientation may be misrecognized.

With transparent films, the boundary with the carrier may not be detected.

With metal foil, the outline can become unstable due to reflection of lighting.

That is why, as necessary,

・Asymmetric cutouts

・Recognition holes

・Alignment marks

・Shapes for distinguishing orientation

・Margins that cameras can easily recognize

are provided.

These are not thermal functions themselves.

However, if the automated machine cannot recognize the correct orientation and position, the thermal function will not be placed in the correct place either.

Adding holes and cutouts for position recognition and transport makes automation easier.

However, in thermal management components, providing holes may

・Reduce the effective heat dissipation area

・Narrow the cross-section through which heat flows

・Concentrate stress

・Shorten insulation distance

・Reduce strength

Therefore, shapes for automation must be placed not just at positions convenient for the equipment,

but at positions with little impact on heat, insulation, and strength.

Design to make automation easier must not impair the original thermal performance.

Thermal management components sometimes become long and narrow to avoid surrounding components.

However, narrow parts have the problems of

・Having a small cross-sectional area through which heat can pass

・Stretching easily during peeling

・Sagging easily during suction pickup

・Twisting easily during transport

・Wrinkling easily during application

・Deforming easily during die-cutting and scrap removal

In other words, narrow bridge-like parts are a bottleneck for heat and, at the same time,

a bottleneck for automated supply.

If possible, widening them

・Connecting with curves

・Adding temporary support parts

・Holding them on the carrier

・Dividing the component

and similar methods must be considered.

When wound onto a reel, components are continuously bent. When transported, they are continuously subjected to vibration and temperature changes. When peeled, they are pulled. When picked up by suction, they receive the force of the nozzle. When applied, compression bonding pressure is applied.

Even if they are correct the moment they come out of the processing machine, components change little by little while passing through these processes.

Automation is not machines repeating the same operation. It is components passing through the process in the same shape and the same position every time. For that, not only processing accuracy but also shape design that looks at the entire process is necessary.

So finally, let us organize the specific items to check in volume production design and the points to watch in each industry.

In the next article (6-7-3), we cover a design checklist, OTIS’s role, and a summary.

 

Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.