Shaving blade for chip site dressing

A shaving or shearing blade utilized in dressing solder joint chip technologies without the use of heat or a copper block wicking process. In essence, any solder debris resulting from the solder shaving process as implemented by the shaving blade is removed through the intermediary of a vacuum arrangement located as an integral structure in the shaving blade so as to inhibit the potential formation of electrical shorts or causing solder damage in subsequent replacement chip joins or other assembly operations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a shaving or shearing blade utilized in 
dressing sites in solder joint chip technologies by removing excess solder 
without the use of heat or a copper block wicking process; to a method of 
implementing the dressing procedure, and to the use of the shaving or 
shearing blade. In essence, any solder debris resulting from the solder 
shaving process as implemented by the shaving or shearing blade is removed 
through the intermediary of a vacuum arrangement which is located as an 
integral structure in the shaving blade so as to inhibit the potential 
formation of electrical shorts or causing solder damage in subsequent 
replacement chip joins or other assembly operations. 
The techniques of removing components from multichip modules, including 
thermal conduction modules and the like, have been well developed in the 
technology. Although several methods for removing components are currently 
in existence, site dress utilizing the wicking action of a copper block 
has always been employed in order to remove excess solder so as to enable 
a new component to be placed on the site. However, when joining the 
component to a new chip site, the contact non-wet failure rate is quite 
considerable. Copper block site dress processes are also involved in their 
implementation and somewhat difficult to implement. Thus, once a component 
is removed from the multichip module, the component must be inspected for 
any bottom layer metallurgy tear-out or similar condition because a copper 
block will not properly dress the site held up by any debris, such as 
particles or other debris caused by solder removal. The copper block(s) is 
normally located on the site and is heated to reflow temperatures to wick 
any excess solder. The copper block frequently requires a time-consuming 
cleaning action prior to reuse. The copper block can be expensive to 
produce and pre-tinning and flux may be required. 
Much of the currently available component-replacement technology, surface 
mount (SMT) and pin-in-hole (PIH) is not directly extendable to replacing 
individual area-array solder ball flip chips (SBFC) on multichip modules. 
Flip-chip replacement offers some unique challenges in addition to those 
encountered in the removing SMT or PIH components. In general, SBFC 
require a more sophisticated replacement technology capable of tight 
parametric control. Conventional chip attachments, in essence, such as 
wire bond or tape automated bonds (TAB), do not readily lend themselves to 
chip replacement, although some progress has been recently made in this 
technology. 
2. Discussion of the Prior Art 
Several chip removal and ref lux-techniques and their attributes have been 
presented and extensively discussed in an article entitled "An Overview of 
Flip-chip Replacement Technology on MLC Multichip Modules"; The 
International Journal of Microcircuits and Electronic Packaging; Volume 
15, Number 3, Third Quarter 1992; pages 113-126. Flip-chip replacement can 
be tailored to satisfy specific conditions and situations. For example, 
removal may be achieved by mechanical means such as by the application of 
torques or ultrasound, or with the aid of a suitable heat source or 
sources, as described in the above-reference article. Mechanical methods 
are preferred, being both simple and capable of higher throughput. 
However, constraints such as proximity to other surface features, chip 
footprint, or the like, often dictate the replacement methods. Also 
considered have been module constraints such as anisotropic thermal 
conductivity, mass, etc. and their effects. It will be demonstrated that 
with the present invention, even under difficult conditions; for instance, 
high degree of constraints, flip-chips can be individually removed and 
rejoined successfully. 
After chip removal, residual solder left on substrate pads is removed. This 
procedure prevents shorts between adjacent pads due to solder accumulation 
at sites which experience multiple replacements. So-called site dressing 
is also necessary to assure joint integrity by maintaining a solder volume 
which optimizes thermal fatigue life. 
Various methods and tools have been utilized in the technology to dress 
sites or otherwise treat locations to remove debris or the like. 
Nolan et al. U.S. Pat. No. 5,216,803 discloses the removal of remnant wire 
bonds from tape automated bonded (TAB) chips, and as such does not address 
specific requirements encountered in the removal of residual solder on 
various sites; for example, such as so-called C4 or controlled collapse 
chip connections which are the frequent interconnections of individual 
area array solder ball flip chips (SBFC) located on multichip modules. 
Venutolo U.S. Pat. No. 4,954,453 discloses a chip removal method utilizing 
heat in order to break the solder interconnect at a uniform height. 
However, the patent does not address itself to the removal of residual 
solder or debris following the removal operation for a chip. 
Brown et al. U.S. Pat. No. 4,768,698 discloses an X-Y table providing a 
quick shear option which is adapted to remove components from printed 
circuit boards which have been heated through the intermediary of a hot 
air nozzle. 
Jensen et al. U.S. Pat. No. 4,152,172 discloses the vinyl scrubbing of 
input/output terminals of semiconductor elements of a semiconductor waver 
for the removal of oxides. 
SUMMARY OF THE INVENTION 
Accordingly, it is a purpose of the present invention to provide a novel 
shaving or shearing blade of a particularly unique design, in which the 
blade is preferably constituted of pre-hardened, cobalt-impregnated 
high-speed tool steel, and which possesses a unitary shaving or shearing 
tip with an integral vacuum arrangement. The vacuum generated at the blade 
tip is implemented to aspirate solder debris produced during the shaving 
process so as to prevent any solder debris from falling on the substrate 
surface during the shaving procedure, and with the blade being machined so 
that the tip thereof can be positioned on the chip site without causing 
damage to other devices or top surface wiring. Moreover, the angle of the 
blade and width from side to side or front to back can be readily modified 
to operate with different top surface architectures of multichip modules. 
In accordance with the invention, the novel shaving or shearing blade can 
be readily mounted on an apparatus providing for an extremely accurate X, 
Y and Z coordinate positioning and movement thereof through either the use 
of a servo system or manual controls, and may optionally be imparted a 
rotational motion. The plane of the substrate may be located by simply 
touching off on three points, then relating the plane to the shaving blade 
and enabling shaving or shearing the site to within a close tolerance of 
the substrate surface. The product thus possesses extremely little 
residual solder and does not require any wicking with a copper block or 
other solder wicking devices, and also does not necessitate the 
application of any heat to reflow temperatures for vacuum reflow systems. 
Inasmuch as the multiple interconnections are planar and possess a known 
amount of solder, another component can be reliably positioned on the 
vacant site. The mechanism is rendered by the shaving blade to have the 
ability to be moved across a site at a preset speed, and any mount housing 
the shaving blade is adapted to be adjustable both horizontally and 
perpendicularly. Depending upon the product type to be processed, the 
ability to accurately control the height of the shaving blade is critical 
to the quality and performance of the shave, and the tool may be equipped 
with optics which can be angled to observe the site being shaved during 
processing. 
Accordingly, it is another purpose of the present invention to provide a 
novel shaving or shearing blade of a specified material for removing 
solder debris from multichip modules from which components have been 
removed. 
A further purpose of the invention is to provide a shaving or shearing 
blade of the type described possessing an integral vacuum arrangement 
which is connectable to a source of vacuum so as to concurrently aspirate 
any solder debris formed at a site during the solder procedure of being 
shaved by the tip of the blade, and to a method of utilizing the inventive 
shaving or shearing blade.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring more specifically to the drawings, the shaving or shearing blade 
10 is essentially constituted of an elongate body or element 12 of 
preferably essentially rectangular cross-section, although a circular 
cross-section or other configuration may also be employed. A front end 14 
of element 12 is angled forwardly and upwardly to provide a planar surface 
16 which is at a predetermined angle a relative to the longitudinal axis 
or extent of elongate element or body 12, and which forms a shaving or 
shearing surface. The angle .alpha. may be within the range of about 
30-60.degree., and as shown, preferably 45.degree., although other angles 
may be suitably employed pursuant to specific applications. The shaving 
tip portion 18 of the front end 14 of the blade is tapered towards a point 
or thin edge 20, and has a width 22a which extends substantially across 
the entire width of front end 14 so as to form a wedge-like straight 
shaving or shearing chisel edge adapted to smoothly shave solder as 
mentioned hereinbefore. At the rearward upper end of the shaving tip 
portion 18, extending from the upper surface 22 thereof is an upwardly and 
rearwardly angled transverse planar surface 24 extending across the width 
of the blade 10. A slotted aperture 26 in surface 24 which is in alignment 
with tip upper surface 22 communicates with an internal channel 32 formed 
in element 12, and which connects with a transverse bore 28 to which there 
may be connected suitable hoses or other connecting devices (not shown) 
leading to a suctioning device for imparting a vacuum to the shaving tip 
portion 18 of the blade 10. 
Further through-apertures 30 may be formed to extend through the elongate 
body 12 of the blade so as to enable mounting thereof to a suitable 
apparatus imparting predetermined X-Y and Z motion thereto, and possibly 
rotation about an angle .O slashed., as is well known in the technology. 
Such apparatus may also incorporate optical means (not shown) which is 
adapted to be attached to the blade device to facilitate observation of 
the surface being shaved by the blade device. 
Preferably, the construction of the shaving blade 10, which is of an 
integral or single-piece structure may be constituted of a pre-hardened 
cobalt-impregnated high-speed tool steel. The blade is designed to be 
easily positioned on a chip site without causing damage to other devices, 
and due to its material composition may be readily reworked, and is 
thereby adapted to be reconditioned and utilized a considerable number of 
time before being worn out and discarded so as to be highly economical. 
Moreover, the blade 10 may be designed to possess differing widths and tip 
angles besides that illustrated so as to be adaptable to different types 
of multichip modules for the removal of solder debris and the like. For 
example, in addition to shaving and vacuuming solder at the 
above-mentioned C4 interconnected components, the blade may be employed on 
any module possessing thin film metallurgy. The blade can also be 
conceivably employed by a user having a requirement to remove a hermetic 
solder seal band for multichip modules; for the removal of wire bond 
interconnections such as for known good dies (KGD); for discrete surface 
mounted device removal; for the direct attachment of components on board 
with a requirement to remove and dress sites; or for any user intending to 
remove any adhesive from the side of die-bonded chips. 
From the foregoing, it becomes readily apparent that the inventive shaving 
or shearing blade which incorporates an integral vacuum arrangement for 
aspirating or suctioning solder debris or the like concurrently with the 
shaving operation is adapted for many diverse applications so as to render 
the process of chip removal and site dress inexpensive and easily 
accomplished in this and other related technologies. 
While the present invention has been particularly described, in conjunction 
with a specific preferred embodiment, it is evident that many 
alternatives, modifications and variations will be apparent to those 
skilled in the art in light of the foregoing description. It is therefore 
contemplated that the appended claims will embrace any such alternatives, 
modifications and variations as falling within the true scope and spirit 
of the present invention.