High-speed-solder-ball-shear-and-pull-tests.pdf - 第6页

force, confirming early observations using high-speed shear testing [2, 5, 16]. For exam ple, the difference of force data at various failure m odes is not si gnificant. In contrast, it can be found that the fract ure en…

(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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half-sine pulse, was selected for all drop testing in this

evaluation [11]. Choosing this drop condition was necessarily

a compromise; too severe and relative assessment of various

constructions and aging exposures would be difficult, and too

gentle could introduce potentially significant solder joint

cyclic fatigue effects.

Figure 14. Board level drop lifetime with thermal aging of

SAC405 on different pad finishes

(a) 0 hour aging (b) Close-up view at location

indicated by rectangle in (a)

indicated by rectangle in (c)

Figure 15. IMC interfacial fracture during drop test with

and without 500 hours aging (SAC405 + ENIG)

BLDT test boards were fabricated with both non-solder-

mask-defined (NSMD) and solder-mask-defined (SMD) pad

geometries. In both cases, the solder-wetted pad diameter was

0.684 mm. Although NSMD is more typical of actual

production circuit boards, SMD has the advantage for this

correlation study that the BLDT fracture locations are more

likely to occur at the package side; this is significant because

solder ball shear/pull testing can only evaluate the package

side fractures as the component is unattached to a PCB. This

paper only reports results for the SMD board configuration.

(a) 0 hour aging (b) Close-up view at location

indicated by rectangle in (a)

indicated by rectangle in (c)

Figure 16. IMC interfacial fracture during drop test with

and without 500 hours aging (SAC405 + OSP)

(a) IMC failure during drop test

(b) IMC fracture failure during HS ball shear (500 mm/s)

(b) IMC fracture failure during HS ball pull (50mm/s)

Figure 17. Cross-sectional comparison of failure fracture

during drop test, HS ball shear/pull tests (OSP, 500 hours)

An extremely abbreviated summary of the drop testing

results is shown in Figure 14, identifying the mean value (8

assemblies per data point) of the drops-to-failure for the test

board assemblies. Repeating observations recorded in earlier

work, the drop fracture strength of devices with an OSP

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