Basic Principles of X-Ray Inspection for BGA’s

Increased Use of BGA’s

Ball Grid Arrays - array of solder ball connections underneath component

Provides many advantages over leaded components– Reduced component size– Increased I/O count– Smaller footprint– Increased performance

characteristics

The Problem with BGA’s

How to verify a solder bond that cannot be observed?

Hidden joints - touch up not possible

Only way to test integrity of joints – Electrical test– Look Under/Video Scope– X-Ray

How X-Rays Work

image

Presence or Absence of Material

wedge objectx-rays x-raysdetector

imagedetectorlow density

high density material

x-raysx-rays

Differences in Material Density

X-ray tube generatesx-ray energy

X-rays absorbed where density exists in sample - remaining x-rays pass through & strike the detector

Detector converts x-rays to visible light, video camera sends image to processor

Image Processor enhances x-ray images for high-resolution viewing

The image you see

How an X-Ray System Works

Solder Connections Under X-Ray Analysis Main characteristic:

uniformity of the connections

If X-ray shows all connections uniformly circular & equal in area - good indication of complete/proper reflow

Nearly all Defects have “Signatures”

Bridging, missing balls, large voids obvious

Other defects subtle Look for pattern in distortion of

size/shape of bond image Operator learns to identify

defect signatures, process problems and quickly make adjustments

May be due to excess paste or flux

Improper rework implicated

Solder splattering due to poor reflow conditions

Defects Identified by X-Ray: Bridging

Look Under Scope Image

Misregistration

Result of errors in component placement Possible issues with solder mask alignment

Insufficient Reflow

More difficult to spot If package misplaced,

ball shape may be elliptical (easier to identify)

Bond distribution not consistent

Can occur in manufacturing process

Usually due to mishandling

Missing Balls

Cold Solder

More difficult to identify Signified by jagged

irregular edge around the perimeter of the solder ball

Solder Voids

Result of moisture in BGA package – must be thoroughly baked out

Problems with solder paste

Huge issue with lead-free solder

Voids a process indicator, not defect unless excessively large

Motorola Study - balls that contain voids up to 24% more reliable than those without voids!

Solder Voids

At 70 kV

Associated with camera used in many X-ray systems

As voltage increased, void artificially appears to expand (bloom)At 50 kV

Makes void appear larger than it really is

Glenbrook systems not subject to voltage blooming

Solder Voids & Voltage Blooming

Potato Chipping/Popcorning

BGA’s outside edge lifts up from a pad

Center joints squashed due to compression under die area

Caused by moisture in BGA or excessive topside temperature

Normal

Potato Chipping

Note distortion/ warpage of ball bonds lower right corner

View through Look-Under scope. Note package peeling away from solder ball

Potato Chipping/Popcorning

Opens (require angled viewing)

Ball smaller than adjacent balls

Pad shadow seen below indicating no contact between ball & pad

Note two unattached spherical shapes unlike oval shapes adjacent to it– indicate no contact

between pad & solder ball

RTX-113HV X-Ray Inspection System Features powerful 80 kV

X-ray tube GTI-5000 image processor

with auto-BGA analysis software

Sees through dense multilayer PCBs & metal capped BGAs

Variable Angle Viewing allows for 45 degree viewing

GTI-5000 Image Processing Software

Provides analysis of BGA defects: bridging, voids, missing balls

Measures BGA ball size, ball roundness & void size

Software identifies any ball outside of set tolerance Includes CPU, Frame Grabber, Software, Color

Monitor

Variable Angled Viewing

Allows for 45 degree viewing X-Ray source is rotated Allows inspection for full

range of hidden BGA defects:– Missing or mis-registered

solder spheres – Misalignments– Gross solder voids – Non-wetting or non-contact

Operating voltage: 120V, 50/60 Hz Energy sensitivity: < than 15kV to >160 kV X-Ray Tube – 80 kVA Resolution: >20 line pairs per millimeter; can easily

resolve a 1 mil bond wire Magnification: 4 - 50x Maximum field of view: 1” diameter circle Maximum PCB size: 27” x 27” (685mm x 685mm)

with PCB manipulator

Specifications: RTX-113HV

Other Real-Time X-Ray Inspection Systems from Glenbrook TechnologiesJewelBox Series

80 or 90kV 5-7, or 10 micron Focal

Spot size 7x-2000x magnification 5 Axis, 360o Positioner

RTX-113

35-52kV 20 line pairs/mm resolution

(up to 100 optional) Variable Angle Viewing

option available

RTX-Mini

40kV 20 line pairs/mm

resolution Truly Portable – can be

hand carried or shipped!

11 Emery AveRandolph, NJ 07869

Tele: (973) 361-8866Fax: (973) 361-9286

szweig@glenbrooktech.com www.glenbrooktech.com

Manufacturer’s RepAaron Caplan

1310 E. Maple AveSterling, VA 20164

(703) 731-8048aaron@gsaservice.com

www.gsaservice.com

11 Emery AveRandolph, NJ 07869

Tele: (973) 361-8866Fax: (973) 361-9286

szweig@glenbrooktech.com www.glenbrooktech.com

Manufacturer’s RepAaron Caplan

1310 E. Maple AveSterling, VA 20164

(703) 731-8048aaron@gsaservice.com

www.gsaservice.com