reballing process controls and...

© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com © 2004 – 2010

Reballing

Process Controls and Cleanliness

DfR Webinar – December 18, 2014

© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com

o Reballing is both ball removal and ball attach

o Ball removal melts off the pre-existing solder balls and prepares

the solder pads for new solder balls

o Ball attachment is the placement of new solder spheres on the

pads and reflowing them to form an intermetallic bond

o All reballers studied use comparable methods for ball attach

Introduction: Reballing Techniques


Reballing Process Controls

o Five reballers employing distinct techniques were

audited during reballing of ball grid arrays

o Reballers identified as A, B, C, D, & E

o This presentation compares observed differences in

o Reballing techniques

o Control of ionic exposure

o Cleaning procedures

o Resulting differences in cleanliness of reballed components


Test Vehicle Selection

o Two devices which each presented a

unique challenge to reballers

o Fine pitch, low mass

o Large plastic package

o Third component to study the impact of

reballing stresses on 1st level

interconnects1

o Flip chip

1J. Arnold et al, “Impact of Reprocessing Technique on First

Level Interconnects of Pb-Free to SnPb Reballed Area Array Flip

Chip Devices,” iMAPs Device Packaging Conference, 2014.


Test Vehicle: Dummy CSP

o Fine pitch, low mass CSP

o 97 I/O, 0.4mm pitch

o 5mm square package,

3.2mm die

o Demands precise tooling

o Requires care in handling


Test Vehicle: Dummy BGA

o Large plastic BGA



15.2mm die

o Susceptible to warpage


o Vitesse VSC3312

crosspoint switch



3mm die

Test Vehicle: Active Flip Chip


o Eight (8) input pair

circuits

o Two 50Ω pull-up

resistors between true

and complement

o Manufacturer specifies

85Ω to 125Ω as

acceptable range

Test Vehicle: Active Flip Chip


o All measurements for all components within 85Ω and 125Ω range in specification o Five (5)

components probed per population

o Eight (8) probe pairs per component

Results: Electrical Characterization


Ball Removal Techniques: Melting and Wicking

o Manual

procedure

o Balls melted with

an iron

o Liquid solder

absorbed with

fluxed wick

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

o 1 or 2 passes with the iron

o Used by Reballers B & D


Ball Removal Techniques: Dissolution in Molten Solder

o Automated

procedure

o SAC305 balls

melted off

package by

contact with SnPb

fountain

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

o Component contacts molten solder

at least twice

o Used by Reballers C & E


Ball Removal Techniques: Dissolution in Molten Solder

o Automated

procedure

o SAC305 balls

melted off

package by

contact with SnPb

wave

o Hot air knife

leveling

o Reballer A

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal


X-Ray Images After Ball Removal

flip-chip x-ray image with examples of key

features indicated. Solder bumps (first level

interconnects) - yellow circles. Plated

through holes in component substrate - red

arrows. Solder pads from which balls have

been removed - blue dotted circles.

Dressed pads on flip chip; solder visible as radiopacity.

Dark pads on left image indicate thicker coverage than

faintly visible pads on right image.


Ball Placement and Attachment

All reballers

surveyed

employed stencils

to align new

solder spheres

with dressed pads

Generic stencil and fixture

Ball placement techniques and tooling are

widely considered trade secrets

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal


o Does reballing the second level interconnects (B) damage

first level interconnects (A)?

Focus


o Upon receipt, components reflowed to simulate assembly

Sample Preparation


o A contour plot is a graphic representation of the relationships among three numeric variables in two dimensions. Two variables are for X and Y axes, and a third variable Z is for contour levels. The contour levels are plotted as curves; the area between curves can be color coded to indicate interpolated values. (1)

o You can interactively identify, label, color, and move contour levels, and change the resolutions of rectangular grids to get better contouring quality and performance

o The plots on the next slide demonstrate that 95% of the time a resistance reading from the reballed population will overlap with that of the non-reballed population. Each plot indicates reballed and control populations of an I/O pair, and all the plots maintain the same behavior with 95% confidence.

1) SAS Institute Inc.,SAS/INSIGHT User’s Guide, Version 8, Cary, NC: SAS Institute Inc., 1999. 752 pp

What are Contour Plots


Results: Electrical Characterization, cont.

Independence of A0-AN0 Resistance for Reballed Fl ip Chip Populations

Mean

Std

95.00 100.0096.00 97.00 98.00 99.000.00

2.50

0.50

1.00

1.50

2.00


Mean

Std

95.50 100.5096.50 97.50 98.50 99.500.00

2.50

0.50

1.00

1.50

2.00


Mean

Std

95.00 100.0096.00 97.00 98.00 99.000.00

2.50

0.50

1.00

1.50

2.00


Mean

Std

97.00 102.0098.00 99.00 100.00 101.000.00

2.50

0.50

1.00

1.50

2.00


Mean

Std

97.25 102.2598.25 99.25 100.25 101.250.00

2.50

0.50

1.00

1.50

2.00


Mean

Std

95.00 100.0096.00 97.00 98.00 99.000.00

2.50

0.50

1.00

1.50

2.00

Independence of A10-AN10 Resistance for Rebal led Fl ip Chip Populations

Mean

Std

95.50 100.5096.50 97.50 98.50 99.500.10

2.60

0.60

1.10

1.60

2.10

Independence of A11-AN11 Resistance for Rebal led Fl ip Chip Populations

Mean

Std

95.00 100.0096.00 97.00 98.00 99.000.00

2.50

0.50

1.00

1.50

2.00

o Contour plots demonstrate overlap between most populations o 95% confidence limit

o Reballer D may be distinguishable from Reballers A and B

o Not distinguishable from Reballers C, E, or control


o Tomographic acoustic micro-imaging (TAMI) performed

o One flip chip per population

o Focused on two interfaces

o Where C4 bumps adhere to pads on the die

o Where C4 bumps adhere to substrate

o No observed gaps, voids, or delamination on reballed or control

components

Results: Scanning Acoustic Microscopy (SAM)


Results: TAMI-SAM, Die to Bump Interface

A B C

Contr

ol

E D


o Computed tomography generates a 3-D model from a

series of x-ray slices

o One flip chip per population

o No cracks or defects observed on reballed or control components

o Some voiding observed at bump to substrate interface

Results: X-ray Computed Tomography (CT)


o Slices through C4 bumps near substrate provide a

snapshot of voiding in the first level interconnects

o Images were threshold corrected in ImageJ

o Enables estimation of percent voiding

Results: CT, Void Measurement


o No industry standard for voiding in C4 bumps

o IPC-A-610E allows for 25% voiding in solder balls

o Voiding was well below 25% for all reballers and control

Results: CT, Measured Voiding in C4 Bumps


BUT WERE THEY CLEAN!!


handlin

g

Sources of Contamination

Contamination

Flux from ball removal

Flux from ball attach

Handling

Rinse water

During cleaning following ball

removal and ball attach

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal flux

flux

rinse

rinse


Contamination: Ball Removal Flux

Reballers use flux over surface of BGA

Manual processes brush on

Robotic processes dip

flux

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal


Ball Removal Flux

IPC J-STD-004

Designator

Flux

Composition

Flux/Flux Residue

Activity Levels Halides

Reballer A ORH1 Organic High Yes

Reballer B ORH0 Organic High No

Reballer C ORH1 Organic High Yes

Reballer D ORH1 Organic High Yes

Reballer E ORM1 Organic Medium Yes


Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

Reballers use either

tacky flux or solder

paste for ball attach

Solder paste

Squeegeed to pads

through stencil

Tacky flux

Applied over whole surface

of BGA

flux

Contamination: Ball Placement Flux


Ball Attach Flux

IPC J-STD-004

Designator

Flux

Composition

Flux/Flux Residue

Activity Levels Halides Stencil

Reballer A ORH1 Organic High Yes Yes

Reballer B ORH0 Organic High No No

Reballer C RMA Rosin Moderate ? No

Reballer D RMA-RA Rosin-Resin Moderate-High ? Yes

Reballer E REL0 Resin Low No Yes


Contamination: Handling

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

ha

nd

ling

o Most reballers

take

precautions to

avoid handling

contamination

o There are

exceptions

Reballer C


Contamination: Cleaning After Ball Removal

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

o Contamination can be introduced

without proper process controls

o Deionization of

rinse water

o Fresh solvent rinse

Reballer D


o Same sources as cleaning after ball removal

Contamination: Cleaning After Ball Attach

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

Fagor FI-120W Door Style Dishwasher, Reballer E

rinse


Cleaning

Performed

Following ball removal

Following ball attach

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

wash

wash


Cleaning Techniques: Wipe

Manually with isopropyl alcohol

Lintless wipe (i.e. Kimwipe)

Brush

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

wash

wash


Cleaning Techniques: Rinse

Spray wash with warm deionized water

Automated technique

Spray

“Swish”

May or may not include a detergent

Requires a bakeout

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

wash

wash


Cleaning: Post Ball Removal

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

wash

Cleaning agent Manner Cleaning Motion Temperature

Reballer A IPA manual wipe room

Reballer B

(time sensitive)IPA manual wipe room

Reballer B

(time insensitive)DI H2O manual wipe warm

Reballer C

(large batch)DI H2O automated spray warm

Reballer C

(small batch)IPA manual brush room

IPA manual wipe room

DI H2O, detergent automated rinse, spray warm

Reballer E DI H2O automated swish warm

Post Solder Sphere Removal

Reballer D

(all devices

cleaned twice)


Cleaning: Post Ball Attach

Device

needs

reballing

Ball

placement

Ball attach

Reballing

complete

Ball

removal Ball

removal Ball

removal

wash

Cleaning agent Manner Cleaning Motion Temperature

Reballer A DI H2O automated rinse, spray warm

Reballer B

(time sensitive)IPA manual wipe room

Reballer B

(time insensitive)DI H2O manual wipe warm

Reballer C IPA manual brush room

Reballer D DI H2O, detergent automated rinse, spray warm

Reballer E DI H2O, detergent automated spray warm

Post Ball Attach


Cleanliness: Ion Chromatography

Metrohm Modular Ion

Chromatography System

IPC-TM-650, 2.3.28

Includes ionic extraction in

diluted isopropanol at 80°C

for 1 hour

Volume of extract limited by size of component

Avoids over-dilution of sample material

CSPs yielded sufficient extract to measure anions

BGAs yielded sufficient extract to measure anions and weak

organic acids


Component Cleanliness: CSP


Component Cleanliness: CSP

(μg/in2) Br- Cl- F- NO3- NO2

- PO43- SO4

2-

Reballer A - 8.07 - 6.08 - - 1.67

Reballer B - 4.18 - 7.37 - - 7.30

Reballer C - 5.04 - 9.56 - - 4.25

Reballer D - 3.27 - 10.37 - - 10.05

Reballer E - 3.55 - 7.66 - - 7.07

Upper Control

Limit 10 2 1 4 4 4 4


Component Cleanliness: BGA


Component Cleanliness: BGA

(μg/in2) Br- Cl- F- NO3- NO2

- PO43- SO4

2- WOA

Reballer A - 5.80 - 0.51 0.40 - - 19.30

Reballer B 6.50 1.90 - 0.57 - - 0.42 21.36

Reballer C 1.81 1.27 - - - - 0.06 24.91

Reballer D - 2.30 0.84 - - - 0.10 35.09

Reballer E 1.18 0.63 - 0.49 0.46 - 0.42 6.13

Upper

Control Limit 10 2 1 4 4 4 4 50


Sources of Contaminants: Chloride (Cl-)

o Incompletely deionized rinse water

o Added to municipal water to control bacterial growth

o Unprotected handling

o Flux residue

o Non “halide-free” fluxes only


Sources of Contaminants: Nitrate (NO3-)


o Ammonium nitrate and urea fertilizer run-off

o Manufacturing residue

o Substrate etched with ammonium nitrate


Sources of Contaminants: Sulfate (SO42-)


o Acid rain

o Manufacturing residue

o Substrate etched with sodium or ammonium persulfate

o Solder mask

o Contact with paper, plastic, or rubber

o Sulfur a part of, or added to, many materials


Conclusions

o Undesirable concentrations of halides were measured on

final reballed components from all studied suppliers

o Flux selection correlates best to ionic contamination

o Consistent with chloride as most common contaminating species

o Consistent with use of halide containing fluxes


CSP Cleanliness and Flux


BGA Cleanliness and Flux


Conclusions, cont.

o Reballers with poor handling control do not exhibit most

elevated contamination

o Reballers with poor control over cleaning procedures do

not exhibit most elevated contamination

o Cleaning technique appears to have little impact


CSP Cleanliness and Cleaning


BGA Cleanliness and Cleaning


Impact

o Contaminants present on reballed components will enter

assembly procedure

o Flux residues will have another opportunity to activate

o Cause of voiding in assembled joints

o X-ray inspection post-assembly revealed no voiding exceeding

IPC-A-610E (25%)

o Can be present as ionic contamination in final product


Impact, cont.

o What’s most concerning is that reballers think they are

performing sufficient cleaning to remove ionic residues

o ROSE measurement of rinse water does not represent on-part

contamination

o Choose higher activity fluxes with false confidence


Acknowledgements

This work was supported by a Small Business Innovation

Research grant from the Office of the Secretary of

Defense.

The author also wishes to thank the participating

reballers for their warm welcome and insight into the

reballing process.

reballing process controls and...

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