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28

Chip Scale Review January • February • 2018

[ChipScaleReview.com]

Surface analysis as a “blueprint” for semiconductor

package manufacturing

By Jaimal Williamson

[Texas Instruments]

a r iou s a n a l y t i c a l t ool s

popularized by what seem

l i ke my r i a d p r i me t i me

c r i me - s c e n e i nv e s t i g a t i o n (CS I )

television shows have glamorized aspects

of materials science and its prowess in

discovering clues to a mystery. Similar

to a CSI, use of analytical tools like

t ime - of-f l ight seconda r y ion ma ss

spectrometry (ToF-SIMS) and X-ray

photoelectron spectroscopy (XPS) can

reduce the time gap to problem solving.

For instance, on account of the surface

sensitivity of ToF-SIMS and XPS, these

tools can guide a packaging engineer

from the ostensibly impossible “finding

a needle in a haystack” scenario to a

more positive outlook of finding the

“elephant in the room” based on tool

detect abilit y at t he nanometer and

monolayer scale. In this analogy (and

focus of the article), the needle in the

haystack scenario is finding the source of

organic contamination forming between

metallic layers within a f lip-chip ball

grid array (FCBGA) build-up substrate

(see

Figure 1

), where the contamination

degrades bonding strength. Like a CSI

where many inst r ument al tools are

used to solve unknowns about a case,

the aforementioned surface-sensitive

analytical techniques facilitated mapping

a bluepr i nt for t he elusive organ ic

species under investigation. Specifically,

leveraging the advantages of the surface

analytical techniques enabled mapping

a blueprint to decipher chemistry of the

contamination despite limited chemical

information from the chemical supplier

due to intellectual property restrictions.

The FCBGA substrate manufacturing

p r o c e s s i s a n i n t r i c a t e s e r i e s o f

sequential steps where the plethora

of organ ic mat e r ia ls u sed t o form

the composite st r uct u re can create

a labyrinth of challenges in meeting

stringent reliability requirements for

automotive and commercial devices.

Interfacial adhesive quality between

layers of the FCBGA substrate is of

utmost importance to ensure reliable

metal-to-metal or polymer-to-metal

bonding. Critical interfaces within the

composite substrate between polymeric

d i e l e c t r i c a nd c o p p e r l aye r s a nd

copper-to-copper interfaces (that are

embedded within substrate interconnect

structures) are examples where organic

contamination can form and become

det rimental to the reliabilit y of the

aforementioned interfaces.

Emp l oy i ng t h e u s e o f s u r f a c e -

sensitive analytical tools like ToF-SIMS

and XPS enabled a synergistic approach

to elucidate surface chemistry between

layers where interfacial quality was

questioned. Specif ically, anomalous

s ub s t r a t e i n t e r c on ne c t s t r uc t u r e s

were inspected, where ToF-SIMS and

XPS identified surface contamination

r e ve a l i ng o r g a n i c f r a gme n t s a nd

chemical functionality associated with

specific process steps of the FCBGA

manufacturing process. With chemical

structure partly known, these details

were correlated to chemistry found in

the material safety data sheet (MSDS)

pertinent to the process step of interest.

This article focuses on unearthing the

source of organic contamination at a

substrate interconnect structure within

an FCBGA substrate. Surface analysis

aided in narrowing the source of the

organic contamination manifesting itself

during a front-end FCBGA substrate

manufacturing process step.

V

Figure 1:

Example of an FCBGA device.

Figure 2:

Chart illustration of ToF normalized intensity vs. organic fragments or ions detected at the anomalous

substrate interconnect structure.