High-speed-solder-ball-shear-and-pull-tests.pdf - 第5页

(a) Ball shear (ENIG) (b) Ball shear (OSP) (c) Ball pull (ENIG) (d) Ball pull (OSP) Figure 9. The sen sitivity of transition level to brittle mode in ball shear and pull tests at d ifferent testing speeds (a) Shear force…

(a) 5 mm/s (ENIG) (b) 5 mm/s (OSP)

(e) 100 mm/s (ENIG) (f) 100 mm/s (OSP)

(g) 250 mm/s (ENIG) (h) 250 mm/s (OSP)

(i) 500 mm/s (ENIG) (j) 500 mm/s (OSP)

Figure 6. Failure mode distribution in ball pull of specimens

with ENIG and OSP pad finishes

Graphical summaries of the solder ball shear and pull

failure mode results are shown in Figures 5 and 6,

respectively. Similar to results of previous studies, a clear

transition occurred between the ductile mode typical of low

shear/pull speeds, and a brittle mode at higher test speeds [1,

2, 8]. Although the failure mode responses are remarkably

similar between the shear and pull testing, the transition from

ductile to brittle occurred at lower speeds in solder ball pull

testing.

Figures 5 and 6 also demonstrate that the samples with an

OSP finish showed an increased incidence of brittle failure

with increased themal exposure. By contrast, the samples with

ENIG plating yielded only a slight increase in brittle fracture

frequency even at the highest test speeds. The different brittle

fracture response between ENIG and OSP may not be

surprising given the comparative IMC growth rates shown in

Figure 3.

Figures 7 and 8 plot the failure mode data in another

format, showing the percentage of brittle failure mode for

each test speed against aging time, excluding the non-solder

related failure mode (pad lift). This transformation allows the

rate of brittle fracture incidence as a function of time and

aging temperature to be described by simple linear curve

fitting. The curve fitting follows the relationship, y = ax + b,

where y is the brittle failure percentage of ball shear and pull

test after aging, x equals aging time, and a represents the

change in brittle mode percentage with aging, and b is the

brittle failure percentage for the zero time sample. It should

be noted that the different slopes are a measure of the

sensitivity of the test system for detecting changes in brittle

fracture with time or test speed. Observe that the line with the

highest slope in each graph represents the optimal test speed

for each sample to detect changes in brittle fracture rate with

time.

(a) Ball shear (ENIG) (b) Ball shear (OSP)

Figure 7. Brittle failure percentage of ball shear tests at

various testing speeds and aging time

(a) Ball pull (ENIG) (b) Ball pull (OSP)

Figure 8. Brittle failure percentage of ball pull test at

various testing speeds and aging time

Figure 9 transforms the linear curve fitting of Figures 7 & 8

into simplified brittle fracture rate response curves versus

solder ball shear and pull test speeds. These graphs provide a

technique to quantitatively define the optimal test speed

(transition point) at which a solder joint fracture is most prone

to shift from ductile to brittle failure mode. Additionally,

Figure 9 can be used to define a recommended test speed for

evaluating brittle solder joint fractures.

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(a) Ball shear (ENIG) (b) Ball shear (OSP)

Figure 9. The sensitivity of transition level to brittle mode

in ball shear and pull tests at different testing speeds

(a) Shear force (10 mm/s) (b) Shear Energy (10 mm/s)

(e) Shear force (500 mm/s) (f) Shear Energy (500 mm/s)

(g) Shear force (1000 mm/s) (h) Shear Energy (1000 mm/s)

(i) Shear force (3000 mm/s) (j) Shear Energy (3000 mm/s)

Figure 10. Ball shear strength and energy of different failure

modes as a function of aging time and test speed

(SAC405 + ENIG)

3.3 Solder Ball Shear/Pull Fracture Force & Energy

Although all of the previous figures relate to qualitative

observations of failure mode, electronics companies would

clearly prefer a quantitative assessment method which is

independent of subjective operator classification, and is

highly repeatable. The introduction of fracture energy as an

alternative measure of solder joint strength (beyond the

conventional force metric) at high shear/pull speeds

represents a major shift in the test equipment industry. A

companion paper in this conference proceedings provides

additional discussion on the fracture energy assessment metric

(see Figures 7 and 8 in [10]).

(a) Pull force (5 mm/s) (b) Pull Energy (5 mm/s)

(e) Pull force (100 mm/s) (f) Pull Energy (100 mm/s)

(g) Pull force (250 mm/s) (h) Pull Energy (250 mm/s)

(i) Pull force (500 mm/s) (j) Pull Energy (500 mm/s)

Figure 11. Ball pull strength and energy of different failure

modes as a function of aging time and test speed

(SAC405 + ENIG)

Figures 10 and 11 provide a graphical summary of the

fracture force and energy data (shear/pull) of SAC405 +

ENIG, while Figures 12 and 13 display the same parameters

for the samples with OSP pad finish. The degree of

correlation between fracture energy and failure mode is

obviously much better than using the traditional measure of

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force, confirming early observations using high-speed shear

testing [2, 5, 16]. For example, the difference of force data at

various failure modes is not significant. In contrast, it can be

found that the fracture energies of various failure modes are

obviously different, both on the specimens with ENIG and

OSP pad finishes as shown in Figures 11 and 13 for ball pull

tests. Specifically, compare histograms (e) and (f) of Figure

11; forces (e) are virtually uniform for all the aging times,

even though failure modes have shifted from ductile to brittle

and pad lift, but there is a distinct shift from high energy

values for ductile failures to lower energies for brittle and pad

lift modes as shown in (f). A similar argument applies to

histograms (c) and (d) in Figure 13. Corresponding examples

can be seen for the shear tests in Figures 10 and 12.

(a) Shear force (10 mm/s) (b) Shear Energy (10 mm/s)

(e) Shear force (500 mm/s) (f) Shear Energy (500 mm/s)

(g) Shear force (1000 mm/s) (h) Shear Energy (1000 mm/s)

(i) Shear force (3000 mm/s) (j) Shear Energy (3000 mm/s)

Figure 12. Ball shear strength and energy for different

failure modes as a function of aging time and test speed

(SAC405 + OSP)

3.4 Board Level Drop Testing

As highlighted in the introduction, the primary objective of

this research was to investigate the feasibility of using high-

speed solder ball shear and pull tests as alternative methods to

board level drop testing for evaluating solder joint integrity

under dynamic loading. In order to provide a basis for

comparison to the shear and pull testing of the components, a

series of drop tests were conducted using board assemblies of

identical package lots evaluated by the DAGE 4000HS.

Moreover, these assemblies were aged at 125

C (0 to 500

hours). It is important to acknowledge, however, that the IMC

composition and morphology for the solder joints are not

identical between the component and assembly aging studies,

due to the rapid dissolution of Cu on the OSP circuit board

during package attachment.

(a) Pull force (5 mm/s) (b) Pull Energy (5 mm/s)

(e) Pull force (100 mm/s) (f) Pull Energy (100 mm/s)

(g) Pull force (250 mm/s) (h) Pull Energy (250 mm/s)

(i) Pull force (500 mm/s) (j) Pull Energy (500 mm/s)

Figure 13. Ball pull strength and energy of different failure

modes as a function of aging time and test speed (SAC405

+ OSP)

Only a small subset of the total test results are represented

in this paper. Indeed, some of the other test samples failed

much earlier in drop testing than the 316 BGA packages

(primarily due to their much larger size and mass), and a drop

test condition was selected to insure that failures did not occur

as soon as the first cycle. Following preliminary studies, a

JEDEC JESD22-B110A service condition A; 500G, 1.0 ms

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