defect analysis workshop

Nordson Test and Inspection Defect Analysis Workshop John Travis

X-ray Inspection Criteria & Common Defect Analysis

WHAT IS THAT!!!!

4

Recognize & Identify Common Defects

Today's Mission

Why X-ray Inspect?

Non-destructive test for optically hidden joints (e.g. BGA’s, QFN’s, Connectors) & internal package details (Ball Bonds, Wedge Bonds)

Field failure analysis Process development Production quality control Set-up changes New Product Introduction (NPI) Verification for Rework

High magnification at Oblique Views Application Support Digital Processing Sub Micron/High Power High resolution (1.3 MP or more) Good separation of similar grey levels within the

x-ray image (65,000 Levels) Oblique views around point of analysis (Rotation) Ease of use

Suggested Requirements for X-ray Inspection

7

NO

RM

AL

VIEW

What are we seeing Here??

8

OB

LIQ

UE

VIEW

What Can we see Here??

9

PCB Pad

BGA

Ball

Solder Paste

Pad

PCB

2 x circles on the x-ray

image show BGA connection are OK

PCB

Solder Paste

BGA

Ball

If open connection, the circle on X-ray image will not be seen

X-Ray “OPEN Connection”

Inspection Logic

Proper BGA Wetting Principles

1. Solder ball is more dense than PCB pad

2. If proper wetting occurs the lighter density PCB pad shares its density with the ball.

3. That being the case, the pad will show up as a lighter color than the ball if a homogenous bond is created.

4. If proper wetting does not occur then the pad will carry it’s own density properties and will show up as a dark mass outside the perimeter of the BGA.

When the two masses do not share a common density, the PCB pad is exposed and an open solder joint is detected as indicated in the image on the left.

BGA Open

Strength of x-ray inspection is being able to look for opens, voiding, fractures and generally monitor production quality.

Also - able to prove to your customer that the reflow quality is good - BGAs are often forgiving of process variations - incl. Pb-free

Combat the frequently heard phrase from your customer - “The boards you sent me do not work! It must be how you soldered the BGA!”

Using XRAY for BGA Inspection

Common BGA Opens Cold Profile or Cold spots (visible solder-paste spheres) Hot Tears; caused by rapid cool down using lead free

paste Head in Pillow Exposed Pad on PCB……..Indicative of Profile not quite

hot enough to create an inter-metallic bond. Could also point to contaminated components.

Excessive Voiding Cracks or Fractures due to stress. Clogged Aperture on stencil Bridging

Head in Pillow

Copyright © Dage 2006

Transition from Hot to cold

BGA Voiding

Hot Tears or Fissures

21 | 00 Month 2009 | Confidential

Hot Tears or Fissures

Sample

Detector Rotates

X-ray Tube

principle – Limited Angle CT or PCT

2D images captured with detector at an angle

No sample size limitation as far as it fits in the X-Ray sample tray-No need to cut the sample

Small area of the sample imaged

Similar reconstruction method to full µCT – produces a CT model with 240 CT slices

No Limitations compared to full µCT

© NordsonDAGE 2012

Slices of BGA with Hot Tears


25 | | Confidential

a)

b)

Importance of Identifying Void Location


Solder voiding only reduced the reliability when the voids were located in the crack path

Types of Common Voids


Example of Champagne Voiding


Recommended BGA Inspection Procedure Always inspect at an Oblique Angle for Opens Check corners – shows lifting or Potato Chipping Work your way into the centre. This will Most likely to be the last point to reflow if any

substantial ∆T is present All terminations should be reasonably circular and

consistent in size Voiding, opens (non-reflow), HIP, Partial Wetting Inspect whole of BGA after rework – gives confidence in

the process

Increasing voiding Check fillets Solder balling

TARGET ACCEPTABLE DEFECT

Inspection Criteria Chip Components

Increasing voiding > 20% Check fillets Insufficient solder


Inspection criteria (LGA)

Heel fillet voiding Joints reflowed Insufficient solder


Inspection Criteria Gull Wings

Increasing voiding Joints reflowed Missing interfaces


Inspection Criteria BGA

Inspection Criteria – Pin-in-Hole Fill

Oblique view > 75% fill required Voiding in hole possible


LGA (QFN)

Acceptable QFN Solder


Insufficient Solder on QFN

Cracks & Breaks Copper tracks or in Solder Joints Die cracks: Fatigue from thermal cycling External stress (dropping) See an absence of material in x-ray image (from lower density) May need oblique view to see

Cracks & Breaks

Normal

(Top Down) View

Oblique View

Cracks In Capacitors

Capacitor Cracks

Fillet Tearing in Lead-Free Joints

BGA Cracks


These devices were blowing up!

Dendrites

The standard micro sectioning methods could not find the problem

Dendrites between Pad and lead-frame on SOT 89 The bond wire is 20 microns diameter so the dendrites are only a few microns

Dendrites at High Magnification

CT Image of Dendrites at High Magnification

Movie of Dendrites at High Magnification


Dendrites


Defective Traces


Through Hole Solder

www.yestechinc.com

Thank You!

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