1. Thermal Polymer Bonding (Diffusion bonding)
Master Smart Systems (SMA)
(Micro System Engineering)
Non-Silicon Based Technology Summer Semester 2014/2015
Prof. Dr. Claas Müller
Presented by
Munir Ahmad Afridi (246487)
18th June 2014
Munir Ahmad Afridi (246487)

2. Flow of Presentation Polymer bonding Thermal Polymer bonding
Types of Thermal bonding
Thermal bonding for Micro-Fluidic channels
Results and Conclusion
References
18th June 2014
Munir Ahmad Afridi [246487]

3. Polymer Bonding
Polymers are joined by welding, adhesive bonding & mechanical fastening.
The choice of process is affected by:
The material to be joined.
The strength of joint required.
Cost of process / Speed.
Production quantity.
Welding processes rely on heat at the joint to melt the adjacent polymer, with a weld forming on cooling.
Welding is an option for thermoplastics, while thermoset rely on adhesive bonding or mechanical fastening. [1]
18th June 2014
Munir Ahmad Afridi [246487]

4. Polymer Bonding Different methods of polymer bonding
Techniques employing an external heat source.
Techniques where heat is generated by mechanical movement.
Techniques which directly employ Electro-Magnetism. [1]
[5]
18th June 2014
Munir Ahmad Afridi [246487]

5. Thermal Bonding What is “ Thermal Bonding ”?
7 May 2018
What is “ Thermal Bonding ”?
“Solid state joining process by which two nominally flat surfaces are joined at an elevated temperature using an applied interfacial pressure”.
Operating temperature 0.5 ~0.8 Tm (Absolute melting point of material being bonded). [2]
Interfacial Pressure must be sufficiently low.
Time (user defined) to ensure satisfactory bonding. [1]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

6. Thermal Bonding (Conti…)
7 May 2018
The mechanism of diffusion bonding
Initial 'point' contact, showing residual layer
Yielding and creep, leading to reduced voids and thinner layer
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

7. Thermal Bonding (Conti…)
Final yielding and creep, some voids remain with very thin layer
Continued diffusion, leaving few small voids
Bonding is complete. [3]
18th June 2014
Munir Ahmad Afridi [246487]

8. Polymer Bonding External(Thermal)
Hot plate welding
The part to be welded by hotplate technology are melted by contact with the heat platen and then precisely pressed together to form a final assembly.
The main advantage of product geometries and sizes can be welded. The process is ideally suited for the welding of complex three-dimensional joint surfaces. [1]
Slow Process : 10 seconds ~ 1 Hour.
Used for welding of water and gas pipes, automotive industry ( fluid reservoirs) and PVC door and window frames.
[4]
18th June 2014
Munir Ahmad Afridi [246487]

9. Polymer Bonding External(Thermal)
Hot bar welding
Technique for sealing of films.
The film is placed on base bar.
Heated metal (Electrically heated) bar applies pressure to the films.
It softens the plastic at the joint and forms
the weld.
Typical time for 100 µm thick skeet is 1-3 seconds.
Special coating (PTFE) to prevent molten
polymer from adhering to them.
Suitable for thickness < 500 µm of polymers or
composites.
Used extensively in packaging industry.
[6]
18th June 2014
Munir Ahmad Afridi [246487]

10. Polymer Bonding External(Thermal)
Impulse Welding
Advance form of Hot bar Welding.
Both heating and cooling regime are controlled whilst the joint is still under pressure
Electricity is used to create heat through a high resistive wire (Nickel-Chromium) encapsulated in non stick coating. [1] ,[7]
[7]
18th June 2014
Munir Ahmad Afridi [246487]

11. Polymer Bonding External(Thermal)
7 May 2018
Hot Gas Welding
Stream of gas (air) passes over an electrically
heated element.
Heated gas stream is directed towards the joint
between two thermoplastics parts, where it melts.
Weld is formed by the fusing of the thermoplastics
parts and the filler.
The filler is composed of the same polymer type.
Portable but slower process.
Quality depends on the skills of the operator.
Typical applications include chemical storage vessels and
pipe works. [1]
[8]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

12. Polymer Bonding External(Thermal)
7 May 2018
Extrusion Welding
Similar to hot gas welding.
Filler material is separately heated in the
barrel of a hand-held screw extruder.
Molten material extruded through a FTFE die into
the joint.
Joint is preheated using a hot gas gun mounted on
the extruder barrel.
Can be used for composites, although bond strength will be
that of the filler and not the composite. [1]
[9]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

13. Polymer Bonding External(Thermal)
Flash Free welding 
Resistance welding that does not use any filler material.
The pieces of polymer to be welded are set apart
at a predetermined distance based on
material thickness, material composition, and
desired properties of the finished weld.
 Current is applied to the metal, and the gap
between the two pieces creates resistance and
produces the arc required to melt the metal.
Once the pieces of metal reach the proper temperature, they are pressed together, effectively forging them together.[1]
[10]
18th June 2014
Munir Ahmad Afridi [246487]

14. Polymer Bonding Internal(Mechanical)
7 May 2018
Vibration Welding
Heat is generated by the mechanical movement
of the components to be joined.
The two parts to be joined are brought into contact under an applied load. One part is constrained whilst the other undergoes a rapid linear reciprocating motion in the plane of the joint.
The heat generated by the friction at the two surfaces creates local melting. Subsequently, the vibration stops, the parts are aligned and the joint is cooled under pressure to consolidate the weld.
Widely used in Automotive industry.[1]
[11]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

15. Polymer Bonding Internal(Mechanical)
7 May 2018
Spin Welding
Generates the heat required for melting by spinning
one part relative to the other while holding the two
parts together under a controlled load.
After a specified length of time, spinning stops
and the joint is allowed to cool.[12]
Only applicable to circular joint areas. [1]
The test geometry is shown in Fig. After molding the first shot part (shown in Fig. 3), it was overmolded with a second polymer in a cavity transfer process in an injection molding machine
[12]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

16. Polymer Bonding Internal(Mechanical)
7 May 2018
Orbital Welding
Unlike spin welding, each point on the surface orbits a different point on the face of the stationary part.
The orbit is of constant rotational speed and is identical for all points on the joint surface.
This motion is stopped after sufficient material is melted and the thermoplastic then solidifies to form a weld. [1]
[13]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

17. Polymer Bonding Internal(Mechanical)
Ultrasonic Welding
Use of high frequency mechanical sound energy to soften or melt the thermoplastic at the joint line.
Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations via the welding horn, usually at a frequency of 20 ~ 40kHz.
Ultrasonic welding is a fast process (weld times are typically less than one second) and can easily be automated.
Used in the automotive, appliance, medical, textile, packaging, toy and electronic markets. [1]
[14]
18th June 2014
Munir Ahmad Afridi [246487]

18. Polymer Bonding Internal(Mechanical)
Friction Stir Welding
Primarily as a means of welding aluminum alloys, but it has subsequently been found to be applicable to the welding of thermoplastics.
Unlike conventional friction welding processes, which rely upon relative motion between the two parts to be welded, friction stir welding involves driving a rotating or reciprocating tool along the joint-line between two fixed components.
An ideal process for continuous joining of sheet or plate. [1]
[15]
18th June 2014
Munir Ahmad Afridi [246487]

19. Polymer Bonding Internal(Electromagnetic)
7 May 2018
Resistive Implant Welding
Heat is generated through the introduction of an electrically conductive implant at the joint, through which a high electric current is passed.
The implant heats up due to resistive losses, softening the surrounding plastic.
The implant remains at the weld, which rules out the use of resistive implant welding for some applications and it has the disadvantage of requiring a consumable implant.
Suited to the joining and repair of gas and water pipes since it can be performed in the field. [1]
[16]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

20. Polymer Bonding Internal(Electromagnetic)
Induction Welding
Heat is generated by an induction field set up either by eddy currents
A work coil connected to a power supply is placed in close proximity to the joint.
As electric current at high frequency passes through the work coil, a dynamic magnetic field is generated whose flux links to the implant.
As the implant heats up, the surrounding thermoplastic softens and melts. If pressure is applied to the joint, a weld forms as the joint cools.
Induction welding is ideal for attaching metalized tops to plastic bottles.[1]
[16]
18th June 2014
Munir Ahmad Afridi [246487]

21. Polymer Bonding Internal(Electromagnetic)
High Frequency Welding
Uses high frequency (13 to 100 MHz) electromagnetic energy to fuse together the materials.
A rapidly alternating electric field is set up between two metal welding bars.
The energy generated by this process causes a temperature increase resulting in the melting of the materials.
Combined with the pressure applied by the clamping of the welding bars, this causes a weld to be formed.
Stationary wallets, life jackets, tents, lorry covers, blood bags for the medical industry and automotive components such as air bags.[1]
[17]
18th June 2014
Munir Ahmad Afridi [246487]

22. Polymer Bonding Internal(Electromagnetic)
7 May 2018
Laser Welding
The laser generates an intense beam of radiation (usually in the infra red area of the electromagnetic spectrum) which is focused onto the material to be joined.
Excites a resonant frequency in the molecule, resulting in heating of the surrounding material.
CO 2 laser radiation is readily absorbed by plastics, allowing joints to be made at high speeds, but limiting the depth of penetration of the beam.
Diode lasers is less readily absorbed by plastics, but these lasers are suitable for performing transmission laser welding.
Possible to create joints in plastics over 1mm thick (with transmission laser welding) at up to at least 20m/min whilst rates of up to 750 m/min are achievable in the CO 2 laser welding of films. [1]
[18]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Mani

23. Polymer Bonding Internal(Electromagnetic)
7 May 2018
Infrared Welding
It uses tungsten filament line heaters as the heat source.
Systems involve bringing the two plastic parts to be joined in close proximity to the infrared source for sufficient time for the parts to become molten, withdrawing the source, and then pushing the parts together to form a weld.
Weld times are reduced, the joints are free from contamination (since it is a non-contact process. [1]
[19]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Mani

24. Polymer Bonding Internal(Electromagnetic)
7 May 2018
Microwave Welding
Most thermoplastics do not experience a temperature rise when irradiated by microwaves.
Insertion of a microwave susceptible implant at the joint line allows local heating to take place.
Suitable implants include metals, carbon or a conducting polymer.
Capability to irradiate the entire component and consequently produce complex three-dimensional joints. Welds are typically created in less than one minute.
Proved to be suitable for joining automotive under-body components and domestic appliance parts.
Operating frequency ~ 2.5 GHz – 3GHz[1]
[20]
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

25. Polymer Bonding Internal(Electromagnetic)
Microwave Welding (Cont…)
Example: PMMA to PMMA bonding
Embossed PMMA and PMMA bonding is possible via thin film Au already deposited on the surface.
[20]
 Using hot embossing technique, micro-channel can be created on the PMMA.
Two substrates were bonded at 10 W for approximately 120 s.
Temperature for Au is 183 °C. Melting point for PM MA is 165 °C. [20]
18th June 2014
Munir Ahmad Afridi [246487]

26. Polymer Bonding Internal(Electromagnetic)
Microwave Welding (Cont…)
Substrates were not affected based on visual examination after the microwave bonding processing.
Thickness of the interfacial layer is approximately 1 μm and is a precise and well-controlled layer.
 Interfacial layer composes of the mixture of Au and carbon, which indicates that the microwave energy melted the Au layer causing localized melting of the PMMA substrates to be bonded.
This bond was shown to hold the substrates together under applied tension greater than (7 kg/cm2). [20]
[20]
18th June 2014
Munir Ahmad Afridi [246487]

27. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices.
7 May 2018
Method for thermally bonding poly(methyl methacrylate)(PM M A)substrates.
Used as substrate material for fabrication of microfluidic devices due to its high mechanical stability, good chemical properties and excellent optical clarity.
CO2 laser has been used to create microchannels in PM MA , wavelength 10.6 µm
and maximum power 25W. Maximum speed of laser beam motion is 640mm/s.
Microchannels width and depth are controlled by varying laser power and scanning speed.
Key Challenge: To realize an effective seal by affixing a cover plate to a substrate containing microfabricated channels.
Direct Thermal bonding approach allow formation of enclosed microchannels with uniform surfaces composed entirely of the same polymeric material.
Bonding temperature is kept at 165  °C for PM MA.
Low pressure is kept for structural integrity (20 kPa).
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

28. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
7 May 2018
Thermal bonding Technique
PM MA sheets are rinse with ethanol and deionized water.
PM MA Sheet were placed between a hotplate and un upper Aluminum plate.
Bonding pressure is kept at 20 kPa.
For better surface quality, Silicon wafer is placed between PM MA and plates.
Steps for bonding:
Bonding Strength = Break Force / Bonding Surface Area
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

29. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
Results
Long characteristic wavelength of CO2 emits radiation continuously.
Not good for generating smaller channels less than 100 µm.
The substrate surface temperature will rise rapidly when laser is focused on it
causing it to melt, then decompose and vaporize, leaving a void in substrate.
SEM of cross-section of PM MA
18th June 2014
Munir Ahmad Afridi [246487]

30. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
Effect of Laser Power
18th June 2014
Munir Ahmad Afridi [246487]

31. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
7 May 2018
Cross Section of Bonded Channels. Beam Speed kept at 25.6 mm/s and the laser power for the microchannels is
0.75 W b) 1.37 W c) 1.5 W
d) W e) 1.75 W f) W
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

32. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
Comparison of the channel dimensions before and after bonding
18th June 2014
Munir Ahmad Afridi [246487]

33. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
Conclusion
CO2 laser micromaching is used to fabricate PM MA mircochannels.
Depths of 150 µm ~ 1500 µm and width of 150 µm ~ 400 µm were achieved adjusting laser power and scanning speed.
High Temperature of 165 °C and low pressure of 20 kPa was kept.
Bonding strength of 2.15 M Pa was achieved.
Good boundary quality is examined.
[22]
18th June 2014
Munir Ahmad Afridi [246487]

34. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices (Conti…)
Microfluidic System [23]
18th June 2014
Munir Ahmad Afridi [246487]

35. Low Pressure, High Temperature Thermal Bonding of Polymeric Microfluidic Devices
[24]
18th June 2014
Munir Ahmad Afridi [246467]

36. References
7 May 2018
Ref[1]: A L Buxton Polymer Technology Group, TWI Ltd Paper presented at the I Mech E seminar, 'The Joining of Plastics and Polymer Composite Materials', held on 24 October 2002 at TWI and published in The Joining of Plastics and Polymer Composite Materials. Ref[2]: Theoretical Model for Diffusion Bonding : B Derby and E.R Walach Ref[3]: diffusion%20bonding.htm Ref[4]: Ref[5]: O.Balkan, H.Demirer, A.Ezdesir, H.Yildirim (2008). Polym.Engin.Sci. 48. p ISSN Ref[6]: Advance Integrated Technology. Ref[7]: Ref[8]: Ref[9]: Ref[10]: Ref[11]: Ref[12]:
18th June 2014
Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

37. References Ref[13]: https://www.youtube.com/watch?v=zLG0H6rlwlw
Ref[20]: Microwave bonding of polymer-based substrates for potential encapsulated micro/nanofluidic
device fabricationKin Fong Lei, Syed Ahsan, Nasser Budraa, Wen J. Li.
Ref[21]: Low-pressure, high-temperature thermal bonding of polymeric microfluidic devices and their
applications for electrophoretic separation
Yi Sun, Yien Chian Kwok and Nam-Trung Nguyen
Ref[22]: Laurie Brown , Terry Koerner , J. Hugh Horton and Richard D. Oleschuk *  Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6
Ref[23]:
Ref[24]:
18th June 2014
Munir Ahmad Afridi [246487]

38. Any question ! ? 7 May 2018 18th June 2014 Munir Ahmad Afridi [246487]
Munir Ahmad Afridi Mani

39. Thank you!
18th June 2014
Munir Ahmad Afridi [246487]