BGA - Ball Grid Array
Inspection Workshop
Bob Willis
leadfreesoldering.com
Mixed Technology Assembly Processes
Adhesive Dispensing
Component Placement
Adhesive Curing
Turn Boar Over
Conventional Insertion
Wave Soldering
Inspection
Inspection Techniques
X-ray inspection procedures
Optical inspection (Endscope)
Destructive mechanical testing
PBGA Reflow
Ceramic Ball Grid Array
Ceramic Column Grid Array
Chip Scale Array
Flip Chip Packages
Flip Chip Package No-flow Underfill
Lead-Free Ball Grid Array
Optical Inspection Systems
ERSA
Optical Inspection Systems
METCAL
Optical Inspection Systems
KH Benz
Kaisertech
Optical Inspection Systems
Optical Inspection Systems
X-Ray Inspection Systems
X-Ray Inspection Systems
Very Skilled Operator
Operator under Training
Design & Layout
Design & Layout
Solder Mask Defined Pads
Design & Layout
BGA Wetting Indicators
BGA X-Ray Assement of Rework
BGA Soldered with Sn/Ag/Cu
BGA X-Ray Assement of Rework
BGA reworked with Sn/Ag/Cu paste
BGA X-Ray Assement of Rework
BGA reworked with Sn/Ag/Cu flux gel
Area Array Alignment Marks
Area Array Alignment Marks
Area Array Alignment Marks
Area Array Alignment Marks
Area Array Alignment Marks
Area Array Alignment Marks
Area Array Alignment Marks
Area Array Alignment
General Inspection of BGA
SIZE OF BALL TERMINATIONS
Ball diameter should be equal to or larger than the original ball
ball diameter on the BGA prior
to reflow due to the addition of paste. In the case of high temperature
temperature lead/tin ball
termination's which do not reflow there should be no change in ball
ball size.
STANDOFF HEIGHT OF BGA PACKAGE.
Measure the difference in height between the board and the base of the BGA laminate on
a minimum of two of the four corners. Compare the variation in height
height of the BGA by
scanning along the length of the BGA on two sides. The height will
will be equal to or less than
the original ball height. The stand off height will reduce due to
to the size of the device and its
weight.
Variations in height between the centre and the edges of the BGA may indicate warpage of
the fibre glass device or PCB. It can also indicate voiding in the
the ball terminations. This is
more commonly noted if all termination measurements are taken. This
This technique is much
simpler with XX-ray as it can be automated. Warpage can occur up or down in the centre
area of the part. Although uncommon warpage can even be seen on ceramic packages.
General Inspection of BGA
CHECK FOR SOLDER SHORTS
Scan along two adjacent sides of a BGA using light from the opposite
opposite side of the devices.
There should be no restrictions to viewing each of the termination
termination outlines. If light is
restricted short circuits may be visible under the device. Viewing
Viewing two sides ensures that
shorts can be seen; viewing one side only shorts can be missed.
Check for complete reflow of solder paste and ball terminations on tin/lead or leadlead-free
joints. In the case of high temperature balls on ceramic parts the
the ball will not become liquid.
During soldering the paste will reflow and allow wetting to take place between the high
temperature ball and the pad surface. There will be a distinct line
line between the ball and the
solder at the interface. This is due to the different metal surfaces
surfaces being joined.
CHECKING FOR CRACKING OR POPCORNING
BGA failures do occur for a variety of reasons, they may be component,
component, printed board,
process or design related. On some occasions both XX-ray and optical inspection can easily
provide the answer and that is when other techniques must be used.
used. Microsections, dye
penetrant and acoustic scans may assist is pinpointing the root cause. The
The essential
aspect in all analysis is the experience of the engineer
BGA Cracking “Popcorning”
BGA Cracking “Popcorning”
BGA Cracking “Popcorning”
BGA Cracking “Popcorning”
BGA Cracking “Popcorning”
General Inspection of BGA
INSPECTION OF BALL GRID ARRAY
Inspection of the solder joints should start at the centre of the
the BGA. This area is the
most likely to be the last point to reflow during soldering. It is the most likely area to
exhibit voids, non reflow or component delamination. If XX-ray is being used after
rework the whole area beneath the part should be scanned.
All BGA termination points should be broadly circular in appearance
appearance and consistent
in size. Measurement of a ball under the centre of the BGA and four
four outer positions
could allow confirmation of complete reflow. These measurements could be
compared with historical data. BGA termination pads may include a wetting
indicator. If this is the case it will make solder joint inspection
inspection easier to assess.
A wetting indicator is a minor change to all pad shapes or a track
track from the mounting
pad which is left exposed. In each case the solder paste can wet away from the main
pad in a controlled manner, wetting may then be confirmed by XX-ray. Use of oblique
angle XX-ray views is ideal as it will often help the investigation of the
the joint interfaces
by allowing a better observation of the interface, this might otherwise
otherwise be obscured if
the view is limited to top down.
BGA Reflow X-Ray
General Inspection Criteria
Inspection Criteria
The following provides a guide to inspection criteria for area array
array solder joints using xx-ray and
optical inspection. The basic criteria are provided for low and high temperature area array
devices.
Ball Grid Array Devices
The ball termination should positioned on the centre of the land,
land, they should not overhang the
pad by more than 25%. The clearance between ball terminations after
af ter reflow should not be less
than the minimum electrical clearance, ball to ball distance.
There should be no evidence of solder shorting under area array devices. Stand off height will
be equal or less than the original ball termination. Measurements
Measurements of stand off height during
production will allow process limits to be defined for any group of devices.
Solder voiding on terminations should be less than 20% of the attachment
attachment area on the pad.
Evidence of complete reflow of solder paste should be seen. Complete
Complete reflow of high
temperature balls or columns may not be visible. Solder joints on
on any one device should have
uniform shape and size and surface appearance which depends on the
the process, materials and
the soldering atmosphere.
General Inspection of BGA
Low temperature ball terminations will show evidence of complete drop of the ball
and paste combining to form a ball shape appearance. High temperature
temperature balls will
have a waist line/demarcation line between the reflowed solder and
and the ball. There
should be some evidence of solder wetting under the high temperature
temperature balls There
should be no evidence of damage to the balls or pads on either the
the component or
printed circuit board.
Variations of ball size over 15% can indicate voiding or compression
compression of balls due to
PCB or package warp. Where present wetting indicators should show
show some
evidence of solder flow. The distance criteria for process control
control can be defined
during production inspection.
Column Grid Array Devices
All columns should be located on the pads, the columns should not
not overhand the
pad surface. Slight deflection of the columns is allowed provided
provided it is still positioned
on the pads. There should be a solder fillet around the complete circumference of
the columns. There should be some evidence of solder wetting under
under the high
temperature columns. The solder should wet to a minimum height of
of 0.010”
0.010”
(0.25mm)
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Via in Pad
Design & Layout Through Via Mounting
Design & Layout Through Via Mounting
Profiling BGA Board Assemblies
One row of balls removed to the centre
Profiling BGA Board Assemblies
Lead-Free BGA with Tin/Lead Paste
BGA Reflowed, balls did not reflow
BGA compressed during reflow
Lead-Free BGA with Tin/Lead Paste
Balls have not reflowed paste has
this is not clear on these images
Lead-Free BGA Optical Inspection
Balls have not reflowed paste has
this is very clear on these images
Lead-Free BGA Optical Inspection
Lead-Free BGA with Tin/Lead Paste
Balls have not reflowed paste has wetted
pads this is shown by the perfect circle
of the xx-ray image
Lead-Free BGA with Tin/Lead Paste
Balls have not reflowed but tin/lead paste
has reflowed and wetted the joints
Plastic Ball Grid Array
High Temperature Terminations
Ceramic Ball Grid Array
Ceramic Column Grid Array
Ceramic Column Grid Array
X-Ray Inspection
BGA
CGA
Chip Component
J Lead
Gull Wing
Leadless Castellation
X-Ray Inspection
The maximum void size in any one
termination will be less than 10%
of that minimum solder joint
dimension. In the case of
multiple voids the maximum area
will be less than 10%.
X-Ray Inspection
Bellcore GR 78
The maximum void size in any one
termination should not exceed 1%
(by volume) on average, with a
worst-case incidence of 5% in less
than one joint per circuit assembly.
X-Ray Inspection
Voids up to 24% of the pad area had
no effect on reliability. They
improved the reliability by 16% when
compared with void free joints.
IPC 610D draft Inspection Criteria
Plastic BGA – Alignment
Target - Class 1,2,3
Placement of the BGA solder ball is centred
and shows no offset of the ball to land centres.
Defect - Class 1,2,3
Solder ball offset violates minimum electrical
clearance.
IPC 610D draft Inspection Criteria
Plastic BGA - Solder Ball Spacing
Acceptable - Class 1,2,3
BGA Solder balls do not violate minimum electrical clearance.
Defect - Class 1,2,3
BGA solder ball spacing violates minimum electrical clearance.
Plastic BGA - Component Height
Acceptable - Class 1,2,3
Overall height CH) of the component does not exceed maximum specified.
specified.
Defect - Class 1,2,3
Overall height of the component exceeds maximum specified.
IPC 610D draft Inspection Criteria
Plastic BGA - Solder Connections
Target - Class 1,2,3
The BGA solder ball terminations are uniform in size and shape.
Acceptable - Class 1,2,3
No solder bridging. BGA solder balls contact and wet to the land forming a continuous
elliptical round or pillar connection.
Process Indicator - Class 2,3
BGA solder ball terminations are not uniform in size, shape, coloration,
coloration, and colour
contrast.
Defect - Class 1,2,3
No visual or xx-ray evidence of solder bridging.
A "waist" in the solder connection indicating that the solder ball
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
connection
IPC 610D draft Inspection Criteria
Plastic BGA – Voids
Acceptable - Class 1,2,3
Less than 10% voiding in the ball to board or ball to component
interface.
Process Indicator - Class 2,3
10-25% voiding in the ball to board or ball to component
interface.
Defect - Class 1,2,3
More than 25% voiding in the ball to board or ball to component
interface.
Mechanical Inspection
Mechanical Inspection
Surface Fibre Contamination
Solder Balls
Excessive Time and Temperature
BGA Optical Inspection
BGA Optical Inspection
Inspection of BGA Board Assemblies
Measure Stand-Off Height
Inspection of BGA Board Assemblies
Measure Stand-Off Height
Inspection of BGA Board Assemblies
Measure Stand-Off Height
Weight will depress balls
Testing Ball Grid Arrays
Testing Ball Grid Arrays
Testing Ball Grid Arrays
Optical Inspection
Optical Inspection
Section View Prior to SEM
X-Ray Examination of Samples
X-Ray Examination of Samples
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Dye Penetration Testing
Poor Pad Solderability
Open Circuit BGA
Voiding PCB Finish Issue
Voiding PCB Finish Issue
www.bobwillis.co.uk
www.leadfreesoldering.com
[email protected]