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Cross section experiment introductionCross section experiment introduction

ECSM QE department

Issue date: Sep. 2006

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Preface-----



. . . . . . . . .



X (X-ray inspection)

(1) BGA Evaluation components: BGA

(2) Inspect for voids or bridges, large/small balls

4.4.3.3 Crossing sectioning: (1) BGA, IC, PTH connector ,Via hole, RLC.

Evaluation components: BGA, IC, PTH connector, Via hole, RLC (2) PTH

Inspection for solder joint structure, crack, void, solder fill conditionof PTH connector.



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(Micro-Cross section):

a) :

b) ()



c)

d) e)

f)



.

1. Cross Section: 2. Resin Powder: 3. Hardener: 4. Sandpaper: 5. Micro-crack: 6. Micro-void:



IPCTM650 2.1.1

1







(fixer) (

()(Hardener)(Resin Powder)



150 600 1200



2000 3000 5000



PCBA2mm

BGABGA

.



2.1

2.2()

2.3 1:1,,1.

2.



2.4

2.5 30

2.6



3.4 3.32000~4000PCB,

3. 3.1 100~150

3.2 0.5mm600

3.3 1200



4. ,1~2



BGA Capacitor

5. a.25x-500X3.35



BGA picture Capacitor picture

b. Cross section result picture



. IPC-7095A Design and Assembly Process Implementation for BGAs

IPC-A-610D Acceptability of Electronic Assemblies

solder bridge

Defect-class 1.2.3

*Visual or X-ray evidence of solder bridge

*Awaistin the solder connection indicating that the solder ball and the attaching solder paste did not flow together

*Incomplete wetting to the land

*BGA solder ball terminations have incomplete reflow of the solder paste

*Fractured solder connection

Surface Mount Area Array-solder connections



Cross section describes the five different void types

MicrovoidsPin Hole VoidsMicrovia VoidsMacrovoids

MacrovoidsShrinkage Voids

MicrovoidsPin Hole VoidsMicrovia VoidsMacrovoids



Solder volume and surface bonding area, It will be necessary to establish an acceptable level voiding so that the product can meet customer expectations, has a useful working life and meets product reliability requirements



Target-Class 1.2.3

*Placement of the BGA solder ball that is centered and shows no offset

Of the ball to land centers:

Defect-Class 1.2.3

*Solder ball offset violates minimum electrical clearance

Acceptance-class 1.2.3

*Overall height (H) of the component does not exceed maximum specified

Defect-Class 1.2.3

* Overall height of the component exceeds maximum specified



There is100% fill

Minimum 75% fill, A maximum of 25% total depression including both secondary and primary sides is permitted

IPC-A-610D Standard requirement



As an exception the fill requirement ,a 50% vertical of PTH is permitted for the products provided following Conditions are met:

The PTH is connected to thermal or conduct planes that act as thermal heat sinks

*The component lead is discemible in the Side B solder connection

*The solder fillet on Side B of the Figure has wetted 3600 of the PTH barrel and 3600 Of the lead

Note: Less than 100% solder fill may not be acceptance in some applications. e.g. thermal shock. The user is responsible for identifying these situations to the manufacturer.



Micro void ()

.

Acceptable-class 1.2.325% or less voiding of the ball X-ray image area

Defect-class 1.2.3More than 25% in the ball X-ray image area



Solder Crack

Solder Joint failure

due to CTE mismatch

PCB

Substrate

Deformed Solder jointdue to warping



PCBSn-0.7CuLift-off



Macro Voids

Planar Micro Voids

Shrinkage Voids

MicroVia Voids

Pin Hole Voids

Kirkendall Voids



(Voiding)(Interface Micro-Voiding)

Reflow(Out gassing)

1. 2. 3. ()4. (Profile)5. 6. 7. PCBABGAQFP



Macro Voids Voids generated by the evolution of volatile ingredients of fluxes and solder pastes Insufficient time to escape 100 to 300 m (4 to 12 mils) in diameterFound anywhere in the solder jointNot Just at Land to solder interfacesNOT unique to SnAgCu (LF) solder jointsEutectic SnPbSnZnXSnBiXAlso called Process voids

IPC Specs 25% max area requirement is targeted toward Macro Voids



Examples of Process Voids in Through Hole Solder Joints



Planar Micro Voids

Micro Voids are smaller than 1-2 mils in diameterMicro Voids are located in one plane at the Landto-solder interface above the Intermetallic compound

These Micro Voids are a risk for reliability failures of BGA and other solder joints



Detection of Micro Voids

Cross-sectional Analysis



Detection of Micro Voids

Pull off solder joint from land



Elongated, voids with rough, `dendritic` edges emanating from the surface of the solder joints

These are seen not just in BGA solder joints, but also in Through Hole Solder Joints and chip component solder joints



Industry consensus is that solidification sequence of SAC solders causes shrink holes

Slow Cooling of solder joints causes excessive shrinkage of the final eutectic solder phase just before solidification Disturbance to the solder joint while it is solidifying will increase amount and size of shrinkage voids

Do not impact reliability

Is not a `Crack` and does not continue to grow under thermo-mechanical stresses

Also called `sink holes` and `hot tears`

Shrink Hole Voids are natural for SnAgCu solders, can be minimized



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vIPCTM650 2.1.1



1



2

BGA



3



4



Cracking in the solder closeto the substrate

Cracking along the interface between the solder and the PCB pad

Breakage of copper trace on PCB



DIP PCB (

PCB



Crack crack

1 2 3 IMC



100X 2000X 2000X

IMC



1.

2.

3. 90

4.

5.

.



6. ,.,:

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b. -------->(),,.,,.

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The end

Thanks !!!



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