Laser releasable temporary bonding film withhigh thermal stability
Yong-suk Yang, Kyo-sung Hwang, Robin Gorrell *3M Korea, 7, Samsung 1-ro 5-gil, Hwaseong-si, Gyeonggi-do, Korea.
*3M Corporation, 6801 River Place Blvd., Austin, TX 78726-9000, United States.

Abstract
A temporary bonding film using a unique, laser releasable

process to be used, carrier coefficient of thermal expansion

pressure sensitive adhesive construction has been formulated(CTE), reusability, and cost.

to advance wafer level fan-out process technology
development. The film format and excellent thermal and3M’s laser releasable temporary bonding film supports

dimensional stability of the temporary bonding film arebonding between semiconductor device and carrier withparticularly well suited to address the developing needs of

excellent adhesion. The benefits of process simplicity and thepanel level fan-out processes. The development of wafer levelhigh level of material heat tolerance achieved with the 3M

packaging process technology provides many benefits,

technology are well aligned with the current direction ofincluding increased density and performance, greater design

packaging technology, with the film format allowing forflexibility, simplification of the supply chain and process, andprocessing of either wafers or large panels. 3M’s laser

improved yield and overall cost of the semiconductor

releasable temporary bonding film employs a glass carrier.

package. Specifically, in the case of fan-out, technology

Laser scanning through the glass carrier enables separation ofadvances allowing wafer thinning to as little as 30 microns,

the carrier without physical stress, allowing thin materials tobackside patterning, and handling of the wafer or panel during

be easily removed from the carrier without physical damage.

copper RDL processing have become possible.

The heat resistance of the 3M temporary bonding film of up to250 ˚C for an extended period allows precise passivation layer

The thinning and handling processes on the molded wafer orcuring and sputtering processes. With the 3M temporary

panel are accompanied by large thermal, physical andbonding film, process designers will be able to implement

chemical stresses. These external stimuli, which are difficult topackage production processes with a wide process margin

overcome with non-rigid semiconductor materials such as

and exceptional quality.

poly-silicone or organic encapsulants, can significantly reduce
the yield of these processes. The most effective approach to

Key Words: Fan-out WLP, Temporary bonding de-bonding

protecting the semiconductor package substrate from thesefilm, RDL-first, RDL-last, Laser releasable film

process stresses is the use of a support carrier. The
combination of a rigid carrier and a semiconductor device
reduces or eliminates physical stresses in the process and cancontrol the warping and expansion or contraction of theI. Wafer level packaging and fan-out WLP
Wafer level packaging technologies are being widely

substrate during thermal exposures. Various carrier materials

adopted in the semiconductor packaging industry

can be used, including thick silicon wafers, glass, ceramics,

based on a variety of benefits, such as enabling smaller

metals and others, with the choice of carrier dependent on a

package form factors, improved thermal and electricalmultitude of factors such as suitability for the carrier release

performance, lower power consumption and lower

Laser releasable temporary bonding film with high thermal stability | 3M

manufacturing cost. Wafer level packaging

force of the temporary bonding film is insufficient, severe device

technologies have led the market beyond existing

warpage occurs during the high temperature process.

packaging technologies such as flip chip ball grid array(BGA) and quad-flat-no leads (QFN) in terms ofII. 3M Laser Releasable Temporary

performance and cost [1]-[2]. The fan-out process has

Bonding Filmalso brought semiconductor micro-patterning

The target format for fan-out technology istechnology into the realm of packaging. Redistribution

transitioning from wafer to panel, particularly atlayers (RDL), implemented with micro-patterning

outourced assembly and test facilities (OSATs) thattechnology and the wafer reconstitution/molding

may not have existing wafer processing infrastructure,process can provide smaller chips and more I/O,

and where the cost advantage of large panel formats up

greatly contributing to maximizing the performance ofto 600 x 600 mm is significant when compared to 200

the package and reducing the production cost. In theor 300 mm diameter wafers. However, in general, spin-

fan-out process, printed circuit board (PCB) interposers

coatable materials that have heretofore been theare no longer needed. The fan-out process can bemainstay of temporary bonding/de-bonding are

divided into RDL-first and RDL-last when considering

difficult to apply in panel applications. On the otherthe RDL build-up process. In the case of an RDL-first

hand, an adhesive in film format is free from theseprocess, where the redistribution layers are formed

limitations. Unlike liquid spin-coatable materials, where

first, and then combined with device chips, the RDL

the bonding material and release material must be

quality does not affect chip loss. This is due the ability

applied to the substrate and carrier through a separate

to inspect or test the RDL and not populate non-process, film-based materials can be easily applied in ayielding sites. However, the RDL-first process itself issimple roll lamination process.

more complicated, requiring a high level of adhesive
surface uniformity to achieve good RDL quality [1]-[3].

3M has developed a family of glass-carrier based, laser
detachable temporary bonding/de-bonding solutions

On the other hand, RDL-last is a process of directly

for the fan-out process (RDL-first process and RDL-lastbuilding RDL on a redistribution wafer prepared byprocess).

picking and placing singulated chips on a temporary
carrier that is overmolded with specially formulated,

Laser releasable temporary bonding film (a multi-

low CTE epoxy molding compound. Cleaning of thelayered product described in the next section) provides

adhesive residue after de-bonding is easy and theexceptional panel/wafer grip performance for the RDL-

process itself is simpler than the RDL-first process.

last process. Strong bending that occurs in thick moldHowever, as shown in Figure 1 below, serious warpage

wafers can be effectively controlled even at highof the mold wafer can occur during curing of thetemperatures over 200 ˚C. In addition, passivationpassivation layers, and is one of the biggest difficulties

curing processes requiring up to 230 ˚C for as long as 4of the current RDL-last process [3].

hours can be carried out. Support for high temperatureprocessing for up to 10 hours is possible if ramp up andramp down are included.
Laser releasable temporary bonding film (a single
layered product) is a laser releasable adhesive film that

Figure 1, Delamination between a carrier and a device due to severe
device warpage during high temperature processing. If the gripping

can be de-bonded with low stress. The laser releasablefilm supports the RDL-first process with excellent
thermal stability and surface roughness uniformity. Pre-2

Laser releasable temporary bonding film with high thermal stability | 3M

aging of the film at 150 ˚C for 30 minutes can increase
the adhesion and physicochemical stiffness of the film
to the carrier. The maximum thermal stability of the

Figure 3, Passivation curing simulation test (230 ˚C X 2hrs X 2 Times)
for actual bonding wafer with 3M product, A) Bonded device withcarrier by using 3M product, B) Maintaining grip force of 3M productlaser releasable layer after thermal aging is up to 300

for glass carrier during passivation layer curing process, C) Mold

˚C. The RDL layer is directly built-up on the adhesive

wafer after carrier de-bonding & adhesive peeling; Device wafer

through the metal deposition and patterning processes

without warpage & adhesive residue.

and the passivation curing process. After the RDL
process is completed, the die is placed onto the RDL
that was built. The laser releasable temporary bonding
film (single layered product) can effectively support the
RDL build-up process and die bonding and molding
processes without delamination [5].

III. RDL-last (chips first) process
3M Laser Releasable Temporary Bonding Film (multilayered product) is a 3 in 1 structure as shown in Figure
2 below. Among the three layers, the bonding layer

Figure 4, TGA Weight loss analysis of 3M Laser releasable temporary
bonding film (multi-layered product): 0.793% @ 230 ˚C for 1hr, N2
Gas

forms the bond to the substrate, and is composed of ahigh molecular weight thermoplastic elastomer, whichshows excellent adhesion to substrates, and withexceptional thermal stability. This allows the temporary
bonding film to support multiple passivation curing
processes without delamination based on its excellent
high temperature wafer grip force. After processcompletion, the adhesive layer can be fully removed
without leaving residue as shown in Figure 3. The
middle layer is a core film for providing structural
support, and selected to minimize CTE and warpage ofthe bonded substrate and carrier. The bottom layer is apressure sensitive adhesive which is bonded to theglass carrier and also provides the laser release
function.

Figure 5, Residue Analysis on mold wafer by GC-Mass

As shown in Figure 3, after a passivation curing
simulation test at 230 ˚C for 4 hours, the laser
releasable temporary bonding film (multi-layered
product) showed excellent wafer bonding performancewith strong wafer grip force. Thermal defects were notfound on the release layer surface. In addition, thetemporary bonding film has demonstrated weight loss
values of less than 1% in thermal gravimetric analysis(TGA) after simulated passivation curing as shown in
Figure 4.

Figure 2, 3M laser releasable temporary bonding de-bonding film
(multi-layered product) for supporting RDL-last process

To check whether adhesive residue remained on thesurface of the mold wafer after thermal processing, themold wafer was cut and put into a capsule containing
solvent and then heated at a high temperature for 4
hours. The solvent was analyzed precisely by gas
chromatography – mass spectrometry (GC-MS) for the3Laser releasable temporary bonding film with high thermal stability | 3M

elements constituting the adhesive. As a result of theevaluation, the corresponding elements were not foundas shown in Figure 5. We could confirm that thetemporary bonding film did not leave adhesive residue
after the passivation layer curing process.

IV. RDL-first process
The RDL-first process can enable better RDL quality

Figure 7, Design concept of 3M laser releasable temporary bonding
film (single layered product)

and lower production cost compared to the RDL-lastprocess. As shown in Figure 6, the RDL-first processbuilds up the RDL directly on the release adhesive
surface, so the adhesive strength and surface
roughness can directly affect the quality of the RDL [4].
Figure 8, Surface roughness analysis of 3M laser releasable
temporary bonding film (single layered product) by Bruker confocal,A) Ra value after glass lamination, B) Ra value after metal deposition(Cu), C) Ra value after thermal aging (@ 210 ˚C for 2hrs)

3M Laser Releasable

Figure 6, 3M Laser releasable temporary bonding film (Single layered
product) for supporting RDL-First process

Condition

Reference**

temporary bondingFilm

As shown in Figure 7 below, the laser releasable
temporary bonding film (single layered product) has alaser active ingredient dispersed to a nano-scale level

Room
Temperature

and a high molecular weight elastomer binder,
providing exceptional thermal stability and excellent

Aging for 1hr

laser de-bonding performance. Numerous polarat 300 ˚C*functional groups in the binder resin also play a majorrole in enhancing interfacial adhesion between the
carrier and the film. Extra functional groups that are not

Table 1, Metal deposition process simulation test of 3M laser
releasable temporary bonding film (single layered product) @ 300 ˚Cinvolved in carrier attachment can be crosslinked tofor 1hr in Air, *Using the flash for clear picture, **Reference sample:

each other through a pre-aging process under high-Initial version laser releasable film

temperature to provide higher thermal stability andchemical resistance [5].

As shown in Figure 8, the initial surface roughness
value of the laser releasable temporary bonding film

The excellent surface uniformity of the laser releasable(single layered product) after lamination onto thetemporary bonding film (single layered product) allows

carrier is very good at 0.087μm. Even after metal

high quality RDL build-up. Generally, to support thedeposition and thermal aging, the Ra value does not

RDL process without any problems, an Ra value of lessexceed 0.2μm, which is also very good. the process forthan 0.5µm is required.

metal deposition is usually carried out under hightemperature and vacuum conditions above 200 ˚C. The
high temperature conditions under vacuum can causemuch larger damage to the organic material than in theatmosphere. We conducted a thermal aging test for the4Laser releasable temporary bonding film with high thermal stability | 3M

laser releasable temporary bonding film (single layered

bonding process, even with laser equipment of the

product) at 300 ˚C to simulate this [6].

same wavelength. For example, if the laser beam width
is wide, lower energy can be required. In general, aAs shown in the lower right image of Table 1, nonarrow beam is often used in a laser marking processdelamination or voiding was observed at the interface

and has a higher energy per unit area than a laser with

between carrier and film, despite the high temperaturewider beam width. In this evaluation, we used a beam

and atmospheric conditions of 300 ˚C. If the adhesive'sof narrow width rather than the normally recommended

adhesion or thermal stability were insufficient, voiding

de-bonding conditions to evaluate the laser blocking

or delamination may occur such as shown in theperformance of 3M products under the most severereference sample. Generally, a 300 ˚C temperature has

conditions. Of course, the condition evaluated (0.4mm

been used for simulating the metal deposition process,

X 20W) is also a condition that results in acceptable de-suggesting that no problems are anticipated in a typicalbonding.

metal deposition process with high vacuum conditionof 220 ˚C [6].

As shown in Figure 10 and Table 2, a 20 watt laser
dosage under the above evaluation conditions was used

V. De-bonding process with laser scanningto carry out the de-bonding process. Unlike the spin

The laser releasable temporary bonding films allow

coated reference material, the temporary bonding film

robust carrier de-bonding processes for lasers ofprovided complete shielding from the laser energy as

various wavelengths. Currently, the temporary bonding

shown by the laser energy detector. The excellent

films can be successfully de-bonded using 308, 355,

barrier performance of the temporary bonding film toand 1,064 nm wavelength lasers. De-bonding islaser energy provides a much wider process margin in

possible without damaging the device with low stressthe design of the fan-out process, and in selection ofas shown in Figure 9.

materials.

Figure 9, Laser de-bonding processing, (A) Laser scanning, (B)

Figure 10, Laser energy blocking performance test, Measure

Demounted device wafer from a carriertransmittance of laser energy by using Laser energy detector (NOVAII)

In addition, 3M laser releasable temporary bonding
3M laser releasable

films can completely block any leaked laser energy
during the de-bonding process. The laser releasable

SampleReference

temporary bonding
film

temporary bonding film exhibits superior laser blocking
performance compared to spin-coatable materials. We
evaluated the laser energy blocking performance of thetemporary bonding film for the most intrusive IR laser(1,064 nm wavelength) under conditions equivalent tothe actual de-bonding process. For reference, a range

Scanning
Energy

10

15

20

10

15

20

3.7

2.7

2.1

0

0

0

(W)
Detected
Energy(W)of process conditions can be acceptable for the de-5Laser releasable temporary bonding film with high thermal stability | 3M

Table. 2, Laser blocking performance evaluation result of 3M Laser[2]

releasable temporary bonding film

Ruben Fuentes, August Miller, and Jonathan Micksch in Amkor
Technology, Inc., “Package assembly design kits bring value tosemiconductor designs”, Chip Scale Review, vol. 22, Number 6,
pp. 39–42, Nov. 2018.

Conclusion
The fan-out process has brought semiconductor micro-[3]

Reliability of Fan-Out Wafer-Level Packaging”, IEEE

patterning technology into the realm of packaging.

TRANSACTIONS ON COMPONENTS, PACKAGING AND

Redistribution Layers (RDL), implemented with micropatterning technology and the wafer

John H. Lau et al., “Design, Materials, Process, Fabrication, andMANUFACTURING TECHNOLOGY.
[4]

Vempati Srinivasa Rao et al., “Development of High Density Fan

reconstitution/molding process can provide smaller

Out Wafer Level Package (HD FOWLP) with Multi-layer Finechips and more I/O, greatly contributing to maximizing

Pitch RDL for Mobile Applications”, 2016 IEEE 66th Electronic
Components and Technology Conference, 978-1-5090-1204-

the performance of the package and reducing the
production cost. Differences in the RDL process, whichis the core of the fan-out process, result in differing

6/16 © 2016 IEEE, DOI 10.1109/ECTC.2016.203, pp. 1522-1529.
[5]

Hong Zhang et al. in Brewer Science, Inc., “Novel Temporary
Adhesive Materials for RDL-First Fan-Out Wafer-Level

process simplification, quality, manufacturing yield andPackaging”, 2018 IEEE 68th Electronic Components andcost. No matter the RDL process used, the support of aTechnology Conference, 2377-5726/18 ©2018 IEEE, DOI

suitable temporary bonding/de-bonding material is10.1109/ECTC.2018.00289, pp. 1925-1930.

required.

[6]

Chia-Hsin Lee et al. in Brewer Science, Inc., “Optimization oflaser release process for throughput enhancement of fan-out

The RDL-first process, which can reduce chip loss andimprove RDL quality, is achieved through the use of awaferlevel packaging”, 2018 IEEE 68th Electronic Components
and Technology Conference, 2377-5726/18 ©2018 IEEE, DOI
10.1109/ECTC.2018.00273, pp. 1818-1823.

single release layer with uniform and low surface
roughness, as well as excellent adhesion [4].
In the case of an RDL-last process, with a simpler
process enabled by building-up the RDL directly on thereconstituted wafer, it is necessary to employ a multilayered type material which can prevent the warpage ofthe device.
The 3M laser releasable temporary bonding film
enables the de-bonding process with low stress, andwithout device damage. The multi-layered film provides
outstanding wafer grip force and the thermal stability
required for an RDL-last process.

Acknowledgment
The authors would like to acknowledge YJ Park of 3M
Korea Analysis lab for analytical supports.

References[1]

Michelle Fowler, Christopher Apanius, and Kimberly Yess in
Brewer Science, Inc., “High-temperature survivability and theprocesses it enables”, Chip Scale Review, vol. 22, Number 6, pp.
14–17, Nov. 2018. (references)6

Laser releasable temporary bonding film with high thermal stability | 3M

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