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 object x-rays detector image detectorlow density high density material x-rays Differences in Material Density

X-ray tube generates x-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: 160 kV  X-Ray Tube – 80 kVA  Resolution: >20 line pairs per millimeter; can easily resolve a 1 mil bond wire  Magnification: x  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 Technologies JewelBox Series  80 or 90kV  5-7, or 10 micron Focal Spot size  7x-2000x magnification  5 Axis, 360 o 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 Ave Randolph, NJ Tele: (973) Fax: (973) Manufacturer’s Rep Aaron Caplan 1310 E. Maple Ave Sterling, VA (703)

11 Emery Ave Randolph, NJ Tele: (973) Fax: (973) Manufacturer’s Rep Aaron Caplan 1310 E. Maple Ave Sterling, VA (703)