Impact test apparatus

An impact test apparatus allows a retaining member to retain a test object. The retaining member is attached to an elastic member. When a weight is made to collide against the test object, impact is applied to the test object. The test object is subjected to free oscillation in response to the impact. The elasticity of the elastic member accepts the movement of the retaining member. Damping of the free oscillation of the test object is minimized. The impact test sufficiently reflects the influence of the free oscillation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impact test apparatus allowing a weight to collide against a test object for testing or measuring the strength of the test object, for example.

2. Description of the Prior Art

Solder bumps are employed to bond a large-scale integrated (LSI) circuit package and a printed wiring board. The solder bumps are arranged to establish a so-called ball grid array (BGA), for example. An impact test is executed so as to evaluate the bonding strength of the ball grid array. Four corners of the printed wiring board are fixed to a support for the impact test. A weight is made to collide against the printed wiring board. Subsequently, electric connection is examined between the printed wiring board and the LSI package.

In general, an electronic apparatus such as a mobile phone terminal suffers from free oscillation after the application of impact of a fall. According to an observation by the present inventor, it has been confirmed that the free oscillation has a large influence on the bonding strength. In a conventional impact test, screws are employed to attach the printed wiring board on the support. It is thus impossible to examine the influence of the free oscillation in the impact test.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide an impact test apparatus enabling to sufficiently reflecting the influence of the free oscillation.

According to a first aspect of the present invention, there is provided an impact test apparatus comprising: a support; an elastic member coupled to the support; a retaining member attached to the elastic member so as to retain a test object; and a weight made to collide against the test object.

The impact test apparatus allows the retaining member to retain the test object. The retaining member is attached to the elastic member. When the weight is made to collide against the test object, impact is applied to the test object. The test object is subjected to free oscillation in response to the impact. The elasticity of the elastic member accepts the movement of the retaining member. Damping of the free oscillation of the test object is minimized. The impact test sufficiently reflects the influence of the free oscillation.

In the impact test apparatus of this type, the allowable distance of relative movement between the retaining member and the test object may be set smaller than that of relative movement between the retaining member and the support. While the retaining member rigidly retains the test object, the elasticity of the elastic member allows the movement of the retaining member. The movement of the test object is thus sufficiently realized. A coil spring may be employed as the elastic member, for example.

According to a second aspect of the present invention, there is provided an impact test apparatus comprising: a support; a first magnet fixed to the support; a second magnet supported on the support for relative movement based on a repulsion between the first magnet and the second magnet; a retaining member attached to the second magnet so as to retain a test object; and a weight made to collide against the test object.

The impact test apparatus allows the retaining member to retain the test object. The retaining member is attached to the second magnet. When the weight is made to collide against the test object, impact is applied to the test object. The test object is subjected to free oscillation in response to the impact. The repulsion between the first and second magnets accepts the movement of the second magnet or retaining member along the support. Damping of the free oscillation of the test object is minimized. The impact test sufficiently reflects the influence of the free oscillation.

In the impact test apparatus of this type, the allowable distance of relative movement between the retaining member and the test object may be set smaller than that of relative movement between the retaining member and the support. While the retaining member rigidly retains the test object, the repulsion between the first and second magnets allows the movement of the retaining member. The movement of the test object is thus sufficiently realized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1schematically illustrates an impact test apparatus11according to a first embodiment of the present invention. The impact test apparatus11includes a support12. The support12includes a base13extending along the horizontal plane, and four support posts14standing upright from the base13, for example. A window opening15is defined in the base13. The base13is immobilized on a support table, not shown, for example. The base13may be made of a metallic material such as aluminum, for example.

The support posts14are fixed to the base13. The individual support posts14include a main elongated body16standing upright from the base13and a pair of upper and lower protrusions17,17protruding from the main body16. The upper and lower protrusions17,17are spaced from each other at a predetermined interval in the vertical direction. The upper and lower protrusions17may be formed integral with the main body16. The upper and lower protrusions17protrude from the support post14in the horizontal direction in parallel with the surface of the base13. The main body16and the protrusions17may be made of a metallic material such as aluminum as a one-piece component, for example.

A pair of elastic members or coil springs18,18are arranged in series between the upper and lower protrusions17,17of the individual support posts14. A retaining member19is interposed between the coil springs18,18. The coil springs18serve to couple the upper and lower protrusions17to the retaining member19. Here, the retaining member19is spaced from the side surface of the main body16at a predetermined interval.

A threaded through bore21is formed in the retaining member19. The retaining member19serves to retain a test object or test sample as described later. A screw may be screwed into the through bore21to retain the text sample, for example. The elasticity of the coil springs18accepts the vertical movement of the retaining member19, namely the test sample, along the main body16.

A high-speed camera22and a light source, namely an illuminator23, are placed at a position below the base13. The high-speed camera22is focused on the test sample placed within the window opening15. Here, the optical axis of the high-speed camera22is aligned with the vertical direction perpendicular to the surface of the base13. The illuminator23is covered with stripes, for example. The illuminator23thus serves to project moiré fringes on the test sample placed within the window opening15. The high-speed camera22serves to capture the image of the projected moiré fringes.

A computer apparatus, not shown, is connected to the high-speed camera22and the illuminator23. The captured image is transmitted to the computer apparatus as image data. In the computer apparatus, the image data is analyzed based on the processing of a software program, for example. Various types of data are generated through the analysis as described later.

A weight24is set at a position above the base13. The weight24may be hung at the height of 1 [m] approximately from the retaining member19, for example. A string25is employed to hang the weight24, for example. The weight24is made to fall toward the base13. A steel ball may be employed as the weight24, for example. The weight of the steel ball may be set at 10 or several dozen grams, approximately, for example. It should be noted that a hammer or a pole may be employed as the weight24in place of the steel ball, for example.

A secondary collision prevention mechanism, not shown, is coupled to the weight24in a conventional manner. The weight24bounces back from the test sample after the collision against the test sample. The secondary collision prevention mechanism allows prevention of a collision of the weight24after the bounce of the weight24. The secondary collision prevention mechanism may be connected to the aforementioned computer apparatus. The computer apparatus may automatically determine conditions such as the fall height and timing of the free fall of the weight24.

Now, assume that impact is applied on the test sample. As shown inFIG. 2, a test sample31is attached to the impact test apparatus11. The test sample31includes a printed wiring board32made of a resin material, for example. Screws33are employed to couple the printed wiring board32to the individual retaining members19, for example. The screw33is screwed into the threaded through bore21of the corresponding retaining member19. The printed wiring board32is in this manner retained on the retaining members19along a horizontal plane, for example.

Referring also toFIG. 3, the test sample31includes a large-scale integrated circuit (LSI) package34mounted on the surface of the printed wiring board32. Solder balls35,35, . . . are employed to bond the LSI package34to an electrically-conductive pad, not shown, of the printed wiring board32. The solder balls35are arranged in a lattice pattern, for example. A so-called ball grid array (BGA) is established based on the solder balls35.

In the impact test apparatus11, the screws33are employed to fix the test sample31to the retaining members19. The coil springs18serve to couple the retaining member19to the corresponding support post14. The allowable distance of relative movement between the test sample31and the retaining member19is thus set significantly smaller than that of relative movement between the retaining member19and the support post14.

As is apparent fromFIG. 3, when the test sample31is attached to the impact test apparatus11, the surface of the printed wiring board32is positioned at a location opposed to the window opening15of the base13. The high-speed camera22is thus focused on the LSI package34and the surface of the printed wiring board32. The illuminator23serves to generate moiré fringes on the surfaces of the LSI package34and the printed wiring board32. The weight24is set at a position directly above the LSI package34, for example.

The weight24is then subjected to a free fall to the upward back surface of the printed wiring board32. The secondary collision prevention mechanism allows the weight24to collide against the back surface of the printed wiring board32only once. The impact of the collision leads to generation of distortion in the printed wiring board32and the LSI package34. The test sample31is subjected to free oscillation by the effect of the distortion. The LSI package34and the printed wiring board32resonate at a specific frequency.

The test sample31is rigidly fixed on the retaining members19with the screws33. The elasticity of the coil springs18thus allows the test sample31to move in the vertical direction along the support post14along with the retaining members19. Such a vertical movement serves to maintain the free oscillation of the test sample31. The elasticity of the coil springs18makes the free oscillation damps as time elapses. After a predetermined duration has elapsed, the printed wiring board32rests.

The high-speed camera22captures an image of the moiré fringes on the surfaces of the LSI package32and the printed wiring board32. The captured image is transmitted to the computer apparatus as image data, for example. The image data is sequentially generated at predetermined time intervals, for example. The computer apparatus operates to specify temporal changes on the deformation of the moiré fringes. The deformation of the LSI package34and the printed wiring board32is in this manner observed. Simultaneously, electric connection is examined between the LSI package34and the printed wiring board32. Damage such as a crack or a fracture to the solder balls35is determined based on the examination of the electric connection.

The impact test apparatus11may accept repetition of the impact test. The same weight24may be made to repeatedly collide against the test sample31, for example. The deformation of the test sample31and the damage to the solder balls35may be examined every time when the weight24is made to collide. The bonding strength is in this manner evaluated between the LSI package34and the printed wiring board32. The service life of the bonding between the LSI package34and the printed wiring board32is calculated based on the bonding strength, for example.

The weights24having different masses may be employed in the impact test in the impact test apparatus11. In this case, test samples of the identical structure may be prepared for the weights24, respectively. The influence of the free oscillation is in this manner evaluated for the individual impact having different magnitudes. The weight24of a sole kind may be made to collide against test samples31having different structures. In this case, the test samples31may have solder balls made of materials having different compositions, for example. The influence of the free oscillation is in this manner evaluated for the solder balls made of materials having different composition.

The impact test apparatus11allows the vertical movement of the test sample31based on the elasticity of the coil springs18. Specifically, the impact makes the test sample31move in the vertical direction. The test sample31is thus allowed to receive an impact almost identical to that of the actual fall. In this case, the printed wiring board32and the LSI package34are subjected to a free oscillation. The elasticity of the coil springs18contributes to minimization of damping of the free oscillation. The impact test sufficiently reflects the influence of the free oscillation after the collision.

In addition, as long as conditions, such as the spring constant and length of the coil springs18and the mass and fall height of the weight24, are maintained, it is possible to repeatedly apply the uniform impact test to the test sample31under the same conditions. The bonding strength of the solder balls35is accurately evaluated, for example. On the other hand, a conventional impact test employs a free fall of the test sample31, for example. This conventional impact test has a significantly low repeatability. The impact test apparatus11according to the present invention contributes to a reduced time required for the impact test.

Furthermore, the computer apparatus is allowed to obtain various types of data, such as deformation amount of the LSI package34and the printed wiring board32, a period of oscillation, a duration of oscillation, and the like, with a higher accuracy, based on the repetition of the aforementioned impact test. Parameters utilized in a numeric simulation for an impact test are derived based on the obtained data, for example. Simultaneously, the damping coefficient of oscillation can be presumed for each component of an electronic apparatus, for example.

FIG. 4schematically illustrates an impact test apparatus11aaccording to a second embodiment of the present invention. The impact test apparatus11autilizes a support12aincluding four support posts41fixed to the base13, for example. The individual support posts41have an L-shaped cross-section. The inner surfaces of the four support posts41,41, . . . are positioned to contour a space of a parallelepiped standing upright on the base13. The support posts41may be made of a metallic material such as aluminum, for example.

A pair of upper and lower first magnets42,42are fixed to the inner surfaces of the individual support posts41. An adhesive or a screw may be employed to fix the first magnets42, for example. The upper and lower first magnets42,42are spaced from each other at a predetermined interval in the vertical direction. A second magnet43is placed in a space between the upper and lower first magnets42,42. The aforementioned retaining member19is attached to the second magnet43. The retaining member19may be held between a pair of magnets, for example.

The first and second magnets42,43may be a permanent magnet, for example. The first and second magnets42,43locate the same poles in opposed relation. The second magnet43is thus allowed to float between the upper and lower first magnets42,42. The repulsion between the first magnets42and the second magnet43accepts the vertical movement of the second magnet43, namely the retaining member19, along the support post41. Like reference numerals are attached to the structure or components equivalent to those of the aforementioned first embodiment.

As shown inFIG. 5, the test sample31is attached to the retaining member19in an impact test. Screws33are employed to attach the test sample31. The retaining member19is supported on the support post14with the first and second magnets42,43. The allowable distance of relative movement between the test sample31and the retaining member19is thus set significantly smaller than that of relative movement between the retaining member19and the support post14.

The weight24is subjected to a free fall to the upward back surface of the printed wiring board32in the same manner as described above. The secondary collision prevention mechanism allows the weight24to collide against the back surface of the printed wiring board32only once. The test sample31is subjected to free oscillation in response to the impact of the collision. Repulsion between the first magnets42and the second magnet43allows the test sample31to move in the vertical direction along the support post41along with the retaining member19. The free oscillation of the test sample31is maintained. The repulsion between the first magnets42and the second magnet43makes the free oscillation damps as time elapses. After a predetermined duration has elapsed, the printed wiring board32rests.

The deformation of the LSI package34and the printed wiring board32is observed based on the image of the moiré fringes captured with the high-speed camera22in the same manner as described above. Simultaneously, electric connection is examined between the LSI package34and the printed wiring board32. The bonding strength is in this manner measured between the LSI package34and the printed wiring board32. The impact test apparatus11ais allowed to enjoy the advantages identical to those obtained in the aforementioned impact test apparatus11.

The test sample31may be soldered to the retaining member19, for example. The spring coefficient and length of the coil springs18and the repulsion between the first and second magnets42,43may depend on the type of the test sample31. These conditions may correspondingly be adjusted. In addition, the first and second magnets42,43may be an electromagnet in place of a permanent magnet, for example. An electronic apparatus such as a mobile phone terminal may be attached to the test sample31, for example. Almost the same impact as an actual impact is in this manner applied in the impact test.