APPARATUS AND METHOD FOR SOLDER BALL FILLING

Field of the invention

The present invention relates to an apparatus and method for solder ball filling a ball grid array (BGA) template.

Description of the Prior Art

Ball grid array techniques are common nowadays for connecting high density integrated circuit (I. C.) components onto circuit boards. Relevant prior art discloses apparatus and methods with regards to filling up a Ball Grid Array (BGA) template with solder balls.

US Patent No. 5,655,704, issued to Matsushita Electric Industrial Co., 12 August 1997 discloses a method of filling a template or a stencil with solder balls as a sweeping solder ball supply bin passes over the template. More particularly as the solder ball supply bin passes over a ball gird array template, any solder balls extending from locating holes provided in the BGA template will come into contact with the sidewalls of the supply bin. These sidewalls impact against the extending solder balls causing them to become damaged and typically broken. The damaged solder balls may then cause faults in the BGA. For example, the damaged or broken solder ball has less material than an undamaged solder balls upon soldering, which results in an ineffective electrical connector being made on the BGA.

To overcome the above mentioned problem, there has been disclosed an apparatus for filling a ball grid array template having a normally horizontal base plate with a BGA template being mounted onto the base plate at one end. A solder ball supply bin is slidably mounted over the surface of the base plate. The bin is enclosed on three vertical sides, while the fourth vertical side proximate the ball grid array template being a pivotable ball gate. At rest, the bin is located at an end of the base plate opposite to the template. When the base is tilted, the bin slides from its rest location to the other end of the base plate, so that it is positioned over the template, thereby allowing the solder balls to fill the locating holes of the template. The base is then rotated in the opposite direction thereby allowing the bin to return to its rest position. As the bin returns to its rest position, the ball gate sweeps any excess balls on the surface of the template back into the bin. A sensing device monitors the position of the ball gate. If the ball gate is

in an open position, this indicates an abnormality in operation. However, a drawback with the known method is that the supply bin does not move completely over the BGA template, otherwise the rear sidewall will break apart any extending soider balls. This means that the operation of the filling apparatus is somewhat slower because a single pass does not result in the supply bin from completely passing over all the locating holes. The supply bin must revert back to the rest position. Consequently, the filling process of the BGA template is slow and less efficient as two tilts of the base piate is required to complete one filling cycle. Furthermore, the tilting of the base plate at a steep angle causes unnecessary agitation of the solder balls, which may lead to an increased rate of oxidization of the solder balls and also results in solder ball damage due to abrasion.

There is a need to provide an apparatus and method for solder ball filling a ball grid array (BGA) template that overcomes, or at least ameliorates, one or more of the disadvantages described above.

SUMMARY

According to a first aspect, there is provided a solder ball filling apparatus comprising: a base plate capable of pivoting between a first pivot direction and a second pivot direction opposite to said first pivot direction; and a ball grid array template provided on the base plate having a plurality of locating holes extending therethrough for receiving solder balls therein; and ^■ a solder ball supply bin having a pair of moveable gates oppositely disposed to ^' each other and respectively connected by a pair of sidewalls to define an enclosure therebetween for holding said soider balls, the solder ball supply bin being mounted on and moveable along said base plate as said base plate pivots between respective first and second directions to enable the solder ball supply bin to pass over the ball grid array template and deposit said balls in the locating holes of said ball grid array template and wherein said pair of moveable gates are arranged to pass over said ball grid array and move upon contact with a solder ball that at least partially extends from said locating holes.

Advantageously, because the pair of moveable gates move upon contact with a solder ball that at least partially extends from said locating holes, the gates do not break the solder balls as the supply bin moves over the ball grid array template. More advantageously because a. pair of moveable gates are provided,

the solder ball supply bin can move completely over the bal! grid array template in both the first and opposite directions without breaking any solder balls that may extend from the locating holes.

The pair of moveable gates may be arranged to pivotally move. Advantageously, the pivotal movement is actuated automatically due to the resistance of the solder ball extending from the locating hole. Therefore, with pivotal movement of the gate, it is not necessary to have separate sensors which detect solder balls that are extending from the locating holes.

The. ball grid array template may be located between two ends of the base plate. Advantageously, the supply bin can completely pass over the ball grid array template in a single pass. In one embodiment, the ball grid array template may be located substantially in the centre of the base plate.

The apparatus may comprise a sensor means for indicating movement of at least one of said moveable gates. Advantageously, ^' the information provided by the sensor indicates that solder balls are extending from the locating holes. This information may be used by an operator of the apparatus to stop the ball filling operation and thereafter remove the protruding solder ball. It is important that the solder ball filling process be precise to ensure that the solder ball array is properly charged with solder balls and thereby ensure good electrical connection of the circuit components in an IC package. As such, a feedback system of sensors is invaluable in detecting errant solder balls which may impair the ball grid array thus formed. In one embodiment, it may be possible to determine when a solder ball is protruding from the ball grid array template by an alarm being set off. Identification of the protruding solder ball may be by means of sensor, such as an optical sensor, .which is configured to set off an audible alarm when a solder bail protrudes from the ball grid array template. The whole ball grid array filling process may then be halted until the error is rectified by removing the protruding solder bali from the ball grid array template.

The sensor means may comprise a pair of sensors respectively arranged to sense movement of said respective pair of moveable gates. The pair of sensors may be disposed at respective ends of the base plate. In one embodiment, the sensor means comprises at least one of a through-beam sensor and a focused beam sensor.

The apparatus may comprise a vacuum source in fluid communication with the locating holes to create a vacuum therein. Advantageously, the vacuum source can be used to pull the solder balls into the locating holes during the solder ball

filling operation. Each of the locating holes may comprise a conduit for being fluidly .coupled to the vacuum source. The vacuum source may be a vacuum pump in fluid communication with the locating holes.

The base plate may be pivoted in at least one of the first and second direction at an angle ranging from about 3 to about 75 degrees, about 5 to about 60 degrees or about 10 to about 50 degrees from the horizontal.

A stop may be provided to prevent the moveabie gate from moving in a defined direction. In one embodiment, the stop is a stop-pin.

. The moveabie gate may be dimensioned to resist movement in at least one of the first and second pivot directions.

The first pivot direction may be in a clockwise direction while the second pivot direction may be in an anti-clockwise direction.

The apparatus of may comprise a ball pick means to remove the solder balls located in said locating holes. The balls may then be transferred to a ball grid array substrate. In one embodiment, the ball pick means comprises a ball pick head may be arranged to be disposed above the ball grid array template and thereby remove said solder balls by vacuum for transfer to a ball grid array substrate.

The supply bin may be moved along the base plate by a motor.

According to a second aspect, there is provided a method of filling a ball grid array with solder balls in an apparatus comprising a solder ball supply bin located on a base plate having a ball grid array template thereon with a plurality of locating holes extending therethrough, the solder ball supply bin having a pair of moveabie gates oppositely disposed to each other and respectively connected by a pair of sidewalls to define an enclosure therebetween for holding said solder balls, the method comprising the steps of:

(a) pivoting the base plate between a first pivot direction and a second pivot direction opposite to said first pivot direction

(b) moving said solder ball supply bin having a plurality of solder balls located therein, along said base plate in the direction of either of said first and second direction and over said ball grid array to deposit solder balls within said locating holes; and

(c) moving at least one of said moveabie gates when in contact with a solder ball extending at least partially from one of the locating holes.

The moving step (c) may comprise the step of (d) pivoting said pair of gates.

The method may further include the step of (e) sensing for movement of at least one of said moveable gates.

The method of may comprise the step of applying a vacuum to said locating holes.

The method may comprise the step of selecting the first pivot direction to be a clockwise direction and the step of selecting the second pivot direction to be an anti-ciockwise direction.

The method may comprise the step of removing the solder balls located in said locating holes for transfer to a ball grid array substrate.

According to a third aspect, there is provided a ball grid array substrate made with solder balls filled on a ball grid array in the method of the first aspect.

DEFINITIONS

The following words and terms used herein shall have the meaning indicated:

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1 % of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1 , 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

FIG. 1 is a cross-sectional schematic view of a solder ball filling apparatus when not pivoting;

FIG. 2 is a cross-sectional schematic view of the solder ball filling apparatus of Fig. 1 when pivoting in a clockwise direction;

FIG.- 3 is a cross-sectional schematic view of the solder ball filling apparatus of Fig. 1 as it is begins to pass over the array of holes in the ball grid array template when pivoting in a clockwise direction;

FIG. 4 shows the solder ball filling apparatus of Fig. 1 as it passes over a ball grid array template when pivoting in the clockwise direction;

FIG. 5 shows the solder ball filling apparatus of Fig. 1 after it has passed over a ball grid array template when pivoting in the clockwise direction;

FIG. 6 shows a bad pick being used to remove solder balls located within the ball grid array template when the base plate is not being pivoted;

FIG. 7 is a cross-sectional schematic view of the solder ball filling apparatus of Fig. 1 when pivoting in an anti-clockwise direction;

FIG. 8 is a cross-sectional schematic view of the solder bali filling apparatus of Fig. 1 as it is begins to pass over the array of holes in the ball grid array template when pivoting in the anti-clockwise direction;

FIG. 9 shows the solder ball filling apparatus of Fig. 1 as it passes over a ball grid array template when pivoting in the anti-clockwise direction;

FIG. 10 shows the solder ball filling apparatus of Fig. 1 after it has passed over a ball grid array template when pivoting in the anti-clockwise direction;

FIG. 11 shows the ball pick being used to remove solder balls located within the ball grid array template when the base plate is restored to an initial position.

DETAILED DESCRIPTION OF THE DRAWINGS

While the specification concludes with the claims defining the features of the invention that are regarded, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawings.

Referring now to FIG. 1 , there is shown an apparatus 10 for filling a ball grid array template 32. The apparatus 10 comprises a base plate 30, capable of rotation about axis 50. The ball grid array template 32 has a plurality of locating holes 34 and is mounted on the base plate 30.

The apparatus 10 also includes a solder ball supply bin 36 carrying a bulk of solder bails 38. The solder bali supply bin 36 has a pair of moveable gates in the form of pivotal front gate 42 and pivotal rear gate 44, which are respectively coupled to each other by sidewalls (not shown) to create a rectangular shaped enclosure in which the solder balls 38 reside. There is no bottom wall provided in the bottom of the supply bin so that the bottom of the supply bin is defined by the upper surface of the base plate 30 and the bali grid array template 32 as the supply bin moves therealong.

The apparatus also includes sensor means in the form of through beam sensor 40 mounted on both ends of the base plate 30. A vacuum source in the form of a vacuum pump (not shown) is in fluid communication with conduit 52 which in turn is in fluid communication with the locating holes 34 provided within base plate 30.

As will be described in further detail below, the base plate 30 is capable of •pivoting in respective clockwise direction 20 (see Fig. 2) and anti-clockwise pivot direction 22 (see Fig. 7), about axis 50. The angle at which the base plate 30 is pivoted can be from about 3 to about 75 degrees, about 5 to about 60 degrees or about 10 to about 50 degrees about the horizontal.

The rectangular-shaped supply bin 36, is driven by a motor (not shown), to slide over and across base plate 30 and ball grid array template 32.

The front gate 42 is pivoted about an axis 46, wherein the gate possesses an innate resistance to anticlockwise moment due to the centre of gravity of the gate being offset from the axis 46(see Fig. 1), thus counter-balancing movement

in the anti-clockwise direction but not to the extent that it wont move in the anticlockwise direction when it experiences a resistance of a protruding solder ball as will be described further below. The gate 42 is however kept in vertical orientation via a stop pin 43 situated beneath the sidewall. Hence, the gate does not tend to pivot but is kept in substantially normal orientation during the movement of the supply bin 36 across the base plate 30 unless it encounters a protruding solder ball extending fully or partially from the locating holes 34 of the BGA template. Likewise, the rear gate 44 is pivoted about an axis 48 and also possesses an innate resistance to clockwise moment due to the weight of the gate at section 44a (see Fig. 1) counter-balancing movement in the clockwise direction as described for gate 42, The gate 44 is also kept in vertical orientation via stop pin 45 situated beneath the sidewall.

The sensor 40 is mounted at a height similar to that of the movable gates (42,44) such that any pivotal movement will be picked up by the sensor. Tilting of the moveable gate indicates obstructions along the path of the supply bin 36 movement wherein the obstructions can result in solder ball filling irregularities on the template 32.

The operation of the apparatus 10 will now be described. Referring to Fig. 1 , the base plate 30 is initially horizontal to allow the solder balls 38 to be loaded into the supply bin 36. However, it should be noted that the loading of the solder balls 38 into the supply bin is not necessarily when the base plate 30 is in the horizontal position. As shown in Fig. 2, the base plate 30 is tilted in the clockwise direction 20 to about 40 degrees above horizontal. The degree of rotation is determined by the propensity of the solder balls 38 to distribute themselves proximally to the gate 42 under gravitational influence. This is to maximize solder ball deposition possibility over the ball grid array template 32 in subsequent steps. The gate 42 is held in position by the stop 43 and forms a close wall to keep the solder balls 38 within the supply bin 36.

Referring now to FIG. 3, the ball supply bin 36 is moved under its own influence by the supply bin motor (not shown) towards the ball grid array template 32. As the supply bin 36 passes over the template 32 the vacuum is being applied to the conduit 52. In other embodiments, the vacuum may not be applied. Hence, the solder balls 38 are deposited into the locating holes 34 as the supply bin 36 moves across the ball grid array template 32.

In the situation whereby a ball-filling anomaly has occurred in that a solder ball extends from the locating hole (see FIG. 4), the gate 44 encounters the

protruding solder ball 54 in its path, causing it to pivot about the axis 48 and thereafter activating the sensor 40. In addition to solder balls, this can be due to foreign matter 58 present in the locating holes 34. Such anomalies can also result from static forces between solder balls, resulting in a solder ball 56 remaining on the ball grid array template 32. In situations whereby the remaining solder balls cannot be easily removed or swept off by the trailing gate, the sensor will be activated accordingly. Advantageously, because the gate 44 moves upon contact with solder ball 54, the gate 44 does not break the solder ball 54 as the supply bin 36 moves over the ball grid array template 32.

Referring now to FiG. 5, after the ball supply bin 36 slides across the template 32, the locating holes 34 will be fully deposited in a way that only one solder ball is contained within one locating hole. Any remaining soider balls that are loosely attached to the ball grid array template 32 can be swept off by the trailing gate 44.

As shown in FIG. 6, the apparatus is subsequently restored to the horizontal position by rotating the base plate 30 about axis 50 in an anticlockwise direction. The solder balls 38 in the locating holes 34 are now suitably oriented for further semiconductor-packaging processes, such as removal via a ball-pick head 60.

To initiate a second filling cycle, the base plate 30 is now pivoted in the anti-clockwise direction 22 at an angle of 40 degrees to the horizontal. The solder balls 38 are accordingly proximally distributed to the gate 44 under the influence of gravity. The gate 44 is held in stop-pin 45 and forms a close wall to keep the solder balls 38 within the supply bin 36.

As shown in FIG. 8, the ball supply bin 36 moves towards the bail grid array template 32. The solder balls- 38 are deposited into the locating holes 34 as the supply bin 36 moves across the ball grid array template 32. The conduit 52 under vacuum further aids this deposition.

As shown in FIG. 10, after the ball supply bin 36 slides across the ball grid array template 32, the locating holes 34 will be fully deposited in a way that only one solder ball is contained within one locating hole. Any remaining solder balls that are loosely attached to the ball grid array template 32 can be swept off by the trailing gate 42. Like the situation described above for Fig. 4, in Fig, 9 the gate 42, upon encountering a protruding solder ball 64 in its path, pivots about axis 46 and thereafter activates the sensor 40. Again, the solder ball 64 does not break due to pivotal movement of the gate 42.

As shown in FIG. 11 , the apparatus is subsequently restored to the horizontal position by rotating the base plate 30 about axis 50 in a clockwise direction.

APPLICATIONS

It will be appreciated that disclosed embodiment of the apparatus and method for solder ball filling a ball grid array (BGA) template, overcome, or at least ameliorate, some of the disadvantages of known methods and apparatuses.

The pair of floating front and rear gates described herein prevent breakage of solder balls extending from the locating holes. This reduces the incidence of damaged or broken solder bails. Accordingly, the disclosed apparatus allows the operator to ensure that the BGA templates are properly filled up and reduces the incidence of damaged solder balls. This in turn overcomes the known soldering problems and results in an effective electrical connector being made on the BGA.

Furthermore, the disclosed apparatus and method allows the supply bin to move completely over the BGA template, thereby filling up the BGA template in one single motion of the ball supply bin. Accordingly, this means that the operation of the filling apparatus can be faster.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respect to be illustrative and not descriptive.