Processing accuracy is a concept indicating how accurately designed shapes, dimensions, positions, thicknesses, and so on can be reproduced.

In thermal management components, for example, the following kinds of accuracy are involved.

・Outer dimension accuracy

・Hole position accuracy

・Lamination position accuracy

・Stacking position accuracy

・Thickness accuracy

・Partial placement accuracy

・Pitch accuracy

・Edge quality

・Burr height

・Flatness

・Warping

・Feed position accuracy within the reel

These do not exist independently.

A defect in one type of accuracy affects other functions.

For example, if the lamination position shifts, the heat source cannot be sufficiently covered.

If the outer dimensions are too large, it interferes with surrounding components.

If it is too thick, it applies excessive pressure to components.

In other words, processing accuracy is a matter of dimensions and, at the same time,

a matter of heat, insulation, assembly, and reliability.

Thermal management materials do not deliver the same effect wherever they are placed inside a product.

The center of the heat source.

Hot spots.

The contact surface with the cooling plate.

The part that passes heat to the enclosure.

They must be placed in such places in the intended state.

For example, suppose a heat-generating component is 10 mm square and the heat dissipation sheet is also 10 mm square.

If the heat dissipation sheet shifts by 1 mm, 10% of the heat source may not be sufficiently covered.

If components become even smaller, the same 1 mm shift has an even greater impact.

In other words, in thermal management, before using high-performance materials,

placing high-performance materials accurately where they are needed is necessary.

The outer shape of a heat dissipation component is not just a matter of appearance.

The outer shape determines

・The area that receives heat

・The area that spreads heat

・The area in contact with cooling components

・The distance to surrounding components

If the outer shape is too small, it cannot sufficiently cover the heat source.

If the outer shape is too large, it interferes with other components, connectors, wiring, and the enclosure.

In addition, with conductive materials, an outer shape that is too large can make insulation distance insufficient.

In other words, outer shape accuracy determines not only whether the part can be assembled,

but also where heat is handled, from where to where.

When a heat dissipation sheet or TIM comes off the heat source, some heat cannot escape sufficiently.

Even if it appears to be in contact on average, if it does not cover the hottest part, the local temperature does not drop.

In semiconductors in particular, the entire chip does not necessarily generate heat uniformly.

Heat generation can concentrate in some parts, such as computing circuits, power supply circuits, and around memory.

That is why it is not necessarily enough to place a thermal management component simply at the center of the component.

Positional accuracy that precisely covers the hot spot is necessary.

Even a slight shift in the application position may change

・Maximum temperature

・Temperature distribution

・Direction of heat spreading

・Thermal effects on surrounding components

Thermal management components have holes and cutouts to avoid screws, connectors, electronic components, and protrusions.

When hole positions shift, not only can the part not be assembled, but the heat path can also become narrower.

For example, if a heat spreading sheet has a large hole, heat must go around it.

If the hole is positioned too close to the heat source, the effective area for spreading heat decreases.

In addition, if a narrow bridge-like part arises, the flow of heat is restricted there.

In other words, holes and cutouts are clearance shapes and, at the same time,

shapes that change the heat path.

When there is a narrow part partway through a heat dissipation component, the amount of heat that can pass through it is limited.

If heat received over a wide area is gathered and made to flow through a narrow shape, thermal resistance becomes high.

This is similar to the idea that resistance increases in narrow parts of electrical wiring.

For example, at

・Between a hole and the outer edge

・Around cutouts

・Narrow connecting parts

・Step avoidance parts

the passage for heat becomes narrow.

Even slight changes in processing dimensions can change the width of these narrow parts and affect thermal performance.

In other words, in fine shapes, not only overall dimensions but also the minimum width through which heat passes is important.

Thermal resistance inside a material is affected by thickness.

For the same material, thermal resistance in the thickness direction generally tends to increase as thickness increases.

That is why, if the thickness of TIM or insulating heat dissipation sheets varies, the thermal performance of each product may also vary.

However, thinner is not necessarily better.

If it is too thin, it cannot absorb steps and warping on component surfaces, and air layers may remain.

If it is too thick, thermal resistance inside the material increases.

In other words, thickness has an appropriate range.

Thickness accuracy is not only about getting close to the target value.

It is stabilizing contact and thermal resistance.

In laminated components, the thickness of each layer accumulates.

Thermally conductive layer.

Insulating layer.

Adhesive layer.

Protective layer.

Even if the thickness of each is within tolerance, the total thickness of the finished product varies.

With components whose total thickness is large, pressure during assembly becomes high.

With components whose total thickness is small, pressure becomes insufficient.

When pressure changes,

・The compression ratio of TIM

・Contact area

・Air layers

・Contact thermal resistance

also change.

In other words, variation in total thickness is not dimensional variation, but variation in contact conditions.

The thickness of soft materials such as TIM, gels, foams, and adhesive materials changes with the pressure applied during measurement.

Measured with strong force, it becomes thinner.

Measured with weak force, it looks thicker.

That is why, even for the same material, results can change depending on the measuring instrument, probe, load, and measurement time.

Even if thickness tolerances are set on the drawing, the numbers may not match between supplier and customer if measurement conditions differ.

In other words, with soft thermal management materials,

not only the thickness value but also under what conditions the thickness was measured must be clarified.

Soft TIM and foams are compressed during assembly.

That is why the free-state thickness differs from the thickness used inside the product.

What directly affects thermal performance is the thickness after assembly.

For example, if a TIM that is 1 mm thick in the free state is compressed to 0.7 mm after assembly, thermal resistance and contact state must be evaluated in the 0.7 mm state.

However, if the compression ratio varies, the actual thickness in use for each product also varies.

In other words, in thickness management, not only thickness after processing,

but also what thickness it will be after assembly must be considered.

Even if the outer shape and thickness of a component are as per the drawing, if there is warping or curl, the entire surface will not be in contact.

Only the center makes contact.

Only the edges lift.

Only one side makes contact.

In such states, contact area decreases and air layers form.

Especially with thin metal foil, graphite, and laminated films, warping can occur due to tension differences and differences in thermal expansion of the materials.

In other words, in thermal management components, flatness is as important as dimensional accuracy.

Warped components are hard to pick up with suction nozzles.

Even if they can be picked up, they fall during transport.

They cannot be positioned correctly against the reference surface.

The edges get caught during application.

As a result, application misalignment and lifting occur.

In other words, warping is not only a thermal performance problem, but also an automated process problem.

In volume production, it is not enough that the component looks flat on its own.

After being peeled from the reel.

When picked up by suction.

When applied.

The shape must be stable in each of these states.

Die-cutting and cutting can produce burrs on edges.

Metal foil burrs.

Film curling.

Adhesive squeeze-out.

Graphite chipping and particles.

When these exist, the component no longer adheres closely to the flat surface.

A small burr can act as a fulcrum and lift the entire component.

As a result, an air layer larger than the burr height may form over a wide area.

In other words, burrs are not just an edge problem.

They are a problem that changes the contact state of the entire component.

With conductive materials such as copper foil, aluminum foil, and graphite, burrs and chipping can cause electrical problems.

Burrs pierce insulating films.

Conductive particles adhere to the surroundings.

Metal edges come close to circuits.

In such states, they may cause short circuits, electrical leakage, and noise.

In other words, with conductive materials for thermal management,

not only heat dissipation performance but also the electrical safety of the edges must be managed.

Adhesive material can squeeze out from the edges due to pressure or temperature.

When adhesive squeezes out, it may

・Change outer dimensions

・Adhere to surrounding components

・Attract foreign matter

・Cause components to stick to each other

・Make automated transport unstable

In addition, if the amount of adhesive squeeze-out differs from product to product, application position and peelability also vary.

In other words, outer shape accuracy is not determined by the dimensions of the base material alone.

It must be managed in the finished state including the adhesive material.

In multilayer components, each layer has a different function.

Heat spreading layer.

Insulating layer.

Adhesive layer.

EMI layer.

Waterproof layer.

When the position of each layer shifts, the necessary function is no longer present where it is needed.

For example, problems arise such as

・The insulating layer shifts and the conductive material is exposed

・The adhesive layer shifts and the fixing area decreases

・The heat dissipation layer shifts and cannot cover the heat source

・The sealing material shifts and the waterproof line is broken

In other words, stacking position accuracy is not accuracy for making things look aligned,

but accuracy for making multiple functions work in the same place.

There are multiple processes before a single finished component is made.

The material is slit.

The first layer is die-cut.

The second layer is laminated.

Outer shape processing is done after lamination.

It is wound onto a reel.

Each process has positional error.

Even if each process is within tolerance, if the errors pile up in the same direction, they may become a large misalignment in the finished product.

This is tolerance stack-up.

That is why, for multilayer, multi-process products, simply allocating the finished product tolerance equally to each process may not be enough.

Which process serves as the reference?

In which process is position corrected?

Which error affects function most?

Processes must be designed with these in mind.

In processing and lamination, what serves as the reference for determining position is important.

Using the outer shape as the reference.

Using holes as the reference.

Using printed marks as the reference.

Using the material edge as the reference.

Using the processed shape from the previous process as the reference.

If the reference is unstable, processing accuracy will not be stable either.

For example, if the material edge is meandering and that edge is used as the reference, component positions will also meander.

In other words, to improve accuracy, not only high-precision equipment,

but also designing a stable reference is necessary.

Even if the center position of a component is correct, its shape may be deformed.

Conversely, even if the shape is correct, the whole thing may be shifted.

For example, even if a circular component is processed to the correct diameter, it will not be sufficiently effective if it is off the center of the heat source.

And even if the center position is correct, if the material stretches into an ellipse, it may interfere with surrounding components.

In other words, in thermal management components,

・Where it is

・What shape it is

must be managed separately.

The dimensions of resin films, adhesive materials, and foams can change with temperature, humidity, and tension.

It matches the drawing during processing, but shrinks after storage.

It stretches during reel transport.

It springs back after being peeled from the release film.

Such changes can change the dimensions of the finished product.

In other words, the processing accuracy of flexible materials is not determined only by the accuracy of blades and dies.

It is necessary to consider how the material moves before and after processing.

The softness, stretch, and adhesiveness of resin materials and adhesive materials can change with temperature and humidity.

When the processing environment changes,

・Dimensions

・Thickness

・Peeling force

・Warping

・Lamination state

may also change.

Results differ between summer and winter.

The adhesive state differs between morning and evening.

Dimensions differ between processing material immediately after taking it out of storage and after letting it acclimate to room temperature.

To prevent such problems, not only processing equipment but also

material storage and the processing environment must be managed.

If one prototype is made and it matches the drawing, it looks as if it can be processed.

In volume production, however, thousands, tens of thousands, or millions of pieces must be made in the same state.

Even if the first piece is right, accuracy may gradually change because

・Blades wear

・Material lots change

・Tension changes

・Adhesive material adheres to equipment

・Temperature changes

・Reel diameter changes

In other words, what matters in volume production is not accuracy that can be achieved once,

but accuracy that does not change even as production continues.

Even if the average processed dimension matches the target value, volume production is not stable if variation is large.

For example, if the target dimension is 10.00 mm, a process in which almost all products cluster around 10.00 mm,

and a process in which they are widely distributed from 9.80 mm to 10.20 mm, differ in quality even though their averages are the same.

In thermal management components too, if variation in

・Contact area

・Application position

・Total thickness

・Compression ratio

・Burr height

is large, product temperatures may also vary.

In other words, in processing accuracy, it is necessary to look not only at whether the average is right, but also at whether the distribution is narrow.

In general dimensional control, it is checked whether things are within tolerance.

With thermal management components, however, it is important to understand how much that tolerance affects thermal performance.

For example, if it is understood

・How many degrees the temperature changes with a positional misalignment of 0.1 mm

・How much thermal resistance changes when thickness increases by 20 μm

・How hot spots change when contact area decreases by 5%

・At how many μm of burr height lifting occurs

then truly necessary tolerances can be set.

In other words, drawing tolerances must be decided not only from the range that can be processed, but from the range in which function can be maintained.

Higher accuracy seems better.

However, tolerances stricter than necessary lead to

・Higher die costs

・Lower processing speed

・More inspection man-hours

・Lower yield

・Higher costs

Strictly controlling even dimensions that do not affect thermal performance may not increase product value.

What matters is not making everything high-precision.

It is identifying the parts that affect thermal performance, insulation, and ease of assembly, and concentrating accuracy there.

Not all dimensions on a drawing are necessarily of the same importance.

For example,

・Positional relationship with the heat source

・Contact area with cooling components

・Insulation distance

・Seal lines

・Suction positions for automated machines

・Reference holes of the component

are of high importance.

On the other hand, parts of the outer perimeter that do not affect heat or assembly may be fine with relatively wide tolerances.

That is why designers and processing manufacturers need to share which dimensions determine function.

Drawings alone may not convey all design intent.

Image inspection is sometimes used to check processing accuracy.

Cameras can check

・Outer shape

・Hole positions

・Application misalignment

・Chipping

・Foreign matter

・Print position, and so on.

However, image inspection alone may not reveal

・Thickness

・Internal air bubbles

・Contact state

・Interlayer delamination

・State after compression

・Thermal resistance

In other words, in inspection, visible dimensions and

invisible functions must be considered separately.

Good appearance and good thermal performance are not the same.

Even if all dimensions are within drawing tolerances, thermal performance drops if there are air bubbles at the contact interface.

Even if thickness is within specification, hot spots remain if there is local uneven compression.

Even if the outer shape is correct, the expected performance will not be achieved if the material’s heat conduction direction is wrong.

In other words, dimensional inspection is important, but it is difficult to fully guarantee thermal performance with it alone.

As necessary, it must be combined with

・Thermal resistance evaluation

・Temperature measurement

・Compression evaluation

・Contact state checks

・Thermal cycle testing, and so on.

In AI servers, many high-heat components, such as GPUs, HBM, power supply components, and optical communication components, are arranged at high density.

Because distances between components are narrow, a slight shift in the outer shape or position of heat dissipation components may cause interference with surrounding components.

In addition, if conductive graphite or metal foil comes too close to circuits, insulation and noise problems also arise.

Furthermore, if the contact height with the cooling plate varies, cooling performance differs from component to component.

In other words, in AI servers,

・Fine outer shape accuracy

・High lamination position accuracy

・Total thickness control

・Flatness control

・Edge control of conductive materials

are important.

In 3D semiconductors and advanced packaging, fine chips and wiring are concentrated in narrow areas.

Thermal management components must also be small, thin, and high-precision.

Even a slight positional misalignment may

・Miss the heat-generating part

・Interfere with surrounding circuits

・Make insulation distance insufficient

・Make bonding pressure uneven

In addition, minute thickness differences can apply local stress to chips and packages.

In other words, in advanced semiconductors, accuracy for thermal performance and

accuracy for not breaking components are needed at the same time.

In EVs and batteries, heat dissipation materials, insulating materials, and sealing materials are used around cells, modules, busbars, and control boards.

Even if components are large, that does not mean accuracy is unimportant.

If insulating material shifts, metal parts are exposed.

If sealing material is cut, moisture gets in.

If the thickness of heat dissipation materials varies, the contact pressure and temperature of each cell change.

In addition, with large components, even a small percentage dimensional difference becomes a large misalignment in absolute terms.

In other words, in EVs and batteries, accuracy that makes wide areas in a uniform state is important.

In smartphones and wearable devices, internal space is extremely limited.

Heat spreading sheets, insulating materials, adhesive materials, and EMI materials are placed in the gaps between components.

Even a misalignment of tens of μm may interfere with

・Cameras

・Batteries

・Antennas

・Flexible printed circuits

・Sensors

In addition, to make surface temperature uniform, graphite and so on must be placed accurately in the intended positions.

In other words, in small devices, processing accuracy simultaneously affects

ease of assembly

thermal performance

communication performance

the user’s perceived temperature.

In medical devices and biosensors, thermal management components are sometimes used close to the human body.

If the application position shifts, the surface temperature may rise locally.

If insulating components shift, safety is affected.

If the adhesive shape is unstable, contact with the skin and the measurement position also change.

In other words, in medical devices, processing accuracy can be directly linked to

measurement accuracy

safety

wearability.

In robots, motors, sensors, wiring, and control components are placed in the narrow space inside joints.

If thermal management components shift, they may interfere with moving parts.

If they are too thick, they apply excessive force to components during assembly.

If they are too small, contact is lost due to vibration.

Furthermore, because robots keep moving, position and contact state must be maintained not only in the initial position but also after operation.

In thermal analysis, material properties and shapes are input.

However, actual products have tolerances.

Component positions shift slightly.

Thickness changes.

Contact area changes.

Warping occurs.

If these are not taken into account, analysis results may not match the temperatures of mass-produced products.

In other words, processing tolerances are not just a manufacturing problem.

They are also design conditions that should be given to thermal simulation.

By assuming maximum and minimum dimensions and positional misalignment rather than analyzing only with ideal dimensions, it becomes easier to predict temperature variation in volume production.

On the shop floor, processing accuracy is checked by dimensional measurement.

However, the original purpose is not to fill in dimension sheets.

Covering the heat source with the same area.

Bringing things into contact with the same pressure.

Ensuring the same insulation distance.

Automatically applying to the same position.

In other words, the essence of processing accuracy is not making the same dimensions,

but repeatedly creating the same thermal function.

When designing and evaluating the processing accuracy of thermal management components, the following must be checked.

・Whether the outer shape can sufficiently cover the heat source

・Whether positional accuracy relative to the hot spot is sufficient

・Whether holes and cutouts narrow the heat path

・How thickness variation affects thermal resistance

・Whether contact pressure changes due to variation in total thickness

・Whether thickness after compression is taken into account

・Whether flatness and warping can be managed

・Whether there are burrs or adhesive squeeze-out

・Whether the insulation safety of conductive material edges is ensured

・Whether the positional accuracy of each laminated layer is sufficient

・Whether tolerance stack-up across processes is taken into account

・Whether material expansion and contraction and temperature/humidity effects are considered

・Whether blade wear during volume production can be managed

・Whether critical dimensions and general dimensions are separated

・Whether the relationship between dimensional accuracy and thermal performance has been checked

・Whether it can be handled stably in automatic application processes

In other words, processing accuracy requires considering drawings, tolerances, materials, processes, inspection, and thermal evaluation together.

In thermal management components, processing accuracy is an important area where OTIS can provide value.

OTIS is not a company that develops thermal materials themselves.

However, by taking high-performance materials and

・Processing them into the necessary outer shapes

・Making shapes that fit the heat-generating parts

・Laminating dissimilar materials in the intended positions

・Managing thickness and steps

・Suppressing burrs and foreign matter

・Supplying them stably in reel form

・Designing them into a state that allows automatic application

we may be able to contribute to reproducing material performance within mass-produced products.

Even high-performance materials will vary in performance from product to product if processing accuracy is not stable.

In other words, OTIS’s role is not changing the performance of materials,

but continuing to create shapes and states in which the performance of materials is not lost.

At OTIS, through

・High-precision die-cutting

・Fine outer shape processing

・Hole and cutout processing

・Half-cut processing

・High-precision lamination

・Lamination of dissimilar materials

・Partial lamination

・Graphite processing

・Copper foil and aluminum foil processing

・Insulating film processing

・Adhesive material processing

・Foam processing

・Narrow-pitch processing

・Reel-to-reel processing

・Reel supply

・Component design for automatic application

・Checking processing conditions, including image inspection

and more, we may be able to contribute to turning thermal management materials into mass-produced parts with stable shapes, positions, and supply conditions.

OTIS is not a company that specializes in

・Formulation development of thermal materials themselves

・Semiconductor chip design

・Thermal design of entire products

・Dedicated CFD analysis

・Design of entire cooling equipment

・Performance assurance of customers’ entire products

However, in the area of repeatedly reproducing in volume production the shapes, thicknesses, and positional relationships required by thermal design, we may be able to play an important role.

★★★★★ AI semiconductors and 3D semiconductors

★★★★★ AI servers

★★★★★ Smartphones

★★★★★ Wearable devices

★★★★★ EVs and batteries

★★★★☆ Medical devices

★★★★☆ Robots

★★★★☆ Optical communications and electronic components

Processing accuracy is the condition for turning material performance into product performance

Thermal management materials have material performance such as thermal conductivity, thermal resistance, and insulation.

However, to make those materials function in actual products,

・The correct shape

・The correct position

・The correct thickness

・The correct laminated state

・The correct contact area

・Stable edge quality

are necessary.

If processing accuracy is unstable,

・The area covering the heat source changes

・Contact pressure changes

・Air layers occur

・The heat path becomes narrower

・Insulation distance changes

・Temperatures vary from product to product

may result.

In other words, processing accuracy is not only making parts as per the drawing.

It is creating the designed flow of heat in the same state for every single product.

In future thermal management, material performance will rise further, and components will become even thinner, smaller, and more multilayered.

At that point, product performance will not be determined by materials manufacturers’ catalog values alone.

How accurately and stably the last few tens of μm can continue to be made will determine the success or failure of thermal management.

 

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.