Soft reworkable thermal gap filling

Thermal Putty for Electronics Gap Filling and Heat Transfer

Haktak supplies thermal putty for assemblies that need soft gap filling, low assembly stress, reworkability and reliable heat transfer across uneven surfaces, variable gaps and compact electronic modules.

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Reworkable TIM Soft gap filling Low stress interface Uneven gap control

Quick answer

What Is Thermal Putty?

Thermal putty is a soft, moldable thermal interface material used to fill gaps between heat sources and cooling surfaces. It conforms to irregular surfaces like a gap filler, but can often remain more reworkable than cured liquid materials. For a broader overview of gap materials, see Haktak’s thermal conductive gap fillers page.

Conform to uneven gaps

Soft putty flows under pressure into local height differences and surface irregularities.

Reduce assembly stress

Low modulus behavior helps avoid excessive load on components, PCBs and sensitive modules.

Support rework

Thermal putty can be useful where the interface may need inspection, repair or replacement.

Application map

Where Thermal Putty Is Used

Thermal putty is used where a soft, formable, thermally conductive material can bridge air gaps without requiring a precisely die-cut pad. It is especially useful in assemblies with component height variation or low pressure limits.

EV Battery and BMS

For battery management electronics, module covers, housings and local heat sources where stress and serviceability matter.

Power Electronics

For converters, MOSFETs, IGBTs, chargers and power supplies that need soft thermal contact to housings or cold plates.

Consumer Devices

For compact electronics, notebooks, handheld devices, SSDs and modules with uneven internal structures.

Industrial Controls

For sensors, controllers, rugged electronics and telecom modules requiring reworkable thermal contact.

Selection logic

How to Choose Thermal Putty

Thermal putty should be selected by gap range, compression behavior, thermal impedance, rework needs and process method. It should not be chosen only by W/mK. Haktak’s blog on why high W/mK does not always mean better cooling is useful background for this point.

Gap rangeMeasure minimum, nominal and maximum gap after tolerance stack-up and assembly.

Thermal targetConfirm component temperature limit, thermal impedance target or benchmark material.

Softness and modulusLower modulus reduces stress but must still maintain contact and placement stability.

ReworkabilityDefine whether the interface needs removal, repair, inspection or field service.

Process methodChoose manual placement, dispensing, pre-forming, stencil or other assembly method.

Reliability risksCheck slump, pump-out, oil bleed, drying, compression change and thermal cycling behavior.

Material comparison

Thermal Putty vs Thermal Pad vs Thermal Grease

Thermal putty sits between pre-formed pads and grease. It is more formable than a pad and better for larger uneven gaps than grease, but it still requires process and reliability validation.

Material	Best Use	Strengths	Watch Points
Thermal putty	Uneven gaps, low pressure interfaces and reworkable assemblies.	Soft, moldable, conformable and suitable for variable component heights.	Check slump, pump-out, oil bleed and placement consistency.
Thermal pad	Defined gaps and repeatable die-cut placement.	Controlled thickness, clean handling and stable geometry. See thermal pads.	May create stress if too thick or too hard for the gap.
Thermal grease	Thin, flat, strongly clamped interfaces.	Low bond line and excellent wetting. See low thermal resistance grease.	Not suitable for large gaps and can pump out under cycling.
Liquid gap filler	Automated dispensing, large area gaps and complex surfaces.	Excellent conformance and flexible process format.	Requires dispensing control, cure or set validation.

Performance parameters

Key Properties That Affect Thermal Putty Performance

Thermal putty performance is controlled by the assembled interface, not only the bulk material. For background, see the blog on thermal conductivity vs thermal impedance and the article on bond line thickness.

Thermal conductivity and thermal impedance at final thickness.
Softness, modulus, compression behavior and contact pressure.
Slump resistance, shape retention and vertical surface stability.
Oil bleed, volatility, drying and long-term material stability.
Dielectric strength, insulation and high-voltage safety margin.
Dispensing, pre-forming, storage and assembly process control.

Design workflow

Thermal Putty Design and Validation Process

Thermal putty should be validated in the real product stack-up. Testing flat coupons alone can miss compression, gap variation, vertical stability and rework behavior.

Measure the gap

Record min, nominal and max gap across components, covers, housings and cooling surfaces.

Select softness

Match modulus and compressibility to the stress limit of PCB, solder joints and components.

Validate placement

Check dispense volume, manual placement, squeeze-out, vertical stability and edge clearance.

Run reliability

Test thermal cycling, vibration, aging, oil bleed, pump-out and rework behavior.

Common mistakes

Common Thermal Putty Selection Mistakes

Thermal putty is forgiving in geometry, but not magic. Poor selection can still cause thermal, mechanical or process problems in production.

Choosing only by W/mK

A high conductivity putty may not cool better if it is too thick, poorly compressed or unstable.

Ignoring slump

Soft materials can move during assembly, storage or high-temperature exposure if shape stability is not checked.

Skipping rework tests

If serviceability matters, removal, residue and replacement behavior should be tested early.

Overfilling the gap

Too much putty may squeeze out or contaminate nearby areas while increasing process variation.

Missing dielectric needs

Power electronics and battery systems may require insulation validation after compression and aging.

Not testing aging

Oil bleed, drying or pump-out can change thermal contact after cycling and high-temperature exposure.

Testing guide

How to Test Thermal Putty

Thermal putty testing should combine thermal, mechanical, process and reliability checks. You can also reference Haktak’s blog on common TIM testing standards for broader validation context.

Thermal testMeasure temperature drop or thermal impedance at actual gap and pressure.

Mechanical testCheck stress transfer, compression, recovery, squeeze-out and dimensional stability.

Process testValidate dispensing, placement, pre-forming, storage, packaging and assembly time.

Reliability testRun thermal cycling, vibration, aging, humidity, oil bleed and pump-out testing.

Rework testInspect removal, residue, cleaning method and replacement performance.

Procurement guide

Information Needed for Custom Thermal Putty

A useful sample request should include the real mechanical and thermal context. Haktak can recommend thermal putty more accurately when the interface gap, stress limit and process method are clear.

Heat source, cooling surface, contact area and target temperature.
Minimum, nominal and maximum gap after assembly.
Required softness, compression range and allowable component stress.
Manual placement, dispensing, pre-forming or automated process requirements.
Dielectric strength, flame rating, silicone-free or low outgassing needs.
Thermal cycling, vibration, aging, pump-out and rework test plan.

Custom supply

Custom Thermal Putty for Production Assembly

Haktak supports thermal putty selection and customization for engineering validation and production assembly. Material properties can be matched for thermal conductivity, softness, reworkability, oil bleed control, dielectric strength and process format.

Material property matching

Match thermal impedance, softness, shape retention, dielectric behavior and reliability requirements.

Process-ready formats

Support bulk, syringe, cartridge, pre-form, liner or custom packaging based on assembly needs.

Engineering sample support

Use drawings, thermal targets and gap data to prepare samples before production validation.

Need Thermal Putty Matched to Your Gap and Assembly Process?

Send your drawing, gap range, heat source, stress limit, rework requirement and reliability plan. Haktak can recommend or customize a thermal putty for your electronics assembly.

Contact Haktak

Selection resources

Thermal Putty Selection Resources for Engineers

Thermal putty is often compared with pads, grease and liquid gap fillers during early design. These internal resources help engineers evaluate material format, gap tolerance, thermal impedance, process method and reliability risk before requesting samples.

Thermal PadsCompare pre-formed pads when the interface needs controlled thickness, clean handling and repeatable die-cut placement. Thermal Conductive Gap FillersReview soft gap filling TIM options for variable gaps, low stress assembly and heat transfer. Liquid Gap FillerUse this page when dispensing, automation or complex surface wetting is more important than reworkability. Thermal GreaseCompare thin bond line compounds for flat, clamped interfaces where large gap filling is not required. Thermal Putty vs Thermal PadBlog guide for uneven gaps, compression limits and tolerance stack-up decisions. Thermal Putty vs Thermal PasteBlog comparison for choosing between moldable putty and thin-interface paste. What Is Thermal Gap Filler?Blog introduction to gap filling thermal interface materials and common use cases. Conductivity vs ImpedanceBlog guide explaining why assembled thermal resistance matters more than W/mK alone.

FAQ

Thermal Putty FAQ

What is thermal putty used for?

Thermal putty is used to fill uneven gaps and transfer heat between components and cooling surfaces while keeping interface stress low.

Is thermal putty better than a thermal pad?

It depends on the gap and process. Putty is useful for uneven or reworkable interfaces, while thermal pads are better for controlled die-cut placement.

Is thermal putty the same as thermal paste?

No. Putty is generally used for larger or uneven gaps, while paste or grease is for thin flat interfaces. See the blog Thermal Putty vs Thermal Paste.

Can thermal putty be reworked?

Many thermal putties are selected for reworkable interfaces, but residue, cleaning and replacement performance should be validated.

Can Haktak customize thermal putty?

Yes. Customization can include thermal conductivity, softness, dielectric behavior, oil bleed control, format and packaging.