IPC-7095C-2013.pdf - 第107页

manual (MXI) and automated (AXI) conﬁgurations. MXI systems can have varying degrees of automation which can include automatic BGA analysis, automatic image process- ing functions, automated manipulation and board handli…

console ﬂoor models. They are also available with a broad

range of X-ray source voltages. There is not a speciﬁc

voltage needed to inspect BGAs. The voltage required will,

in part, depend on the sensitivity of the particular X-ray

system employed, as well as the structure and characteris-

tics of the BGA under inspection. BGAs with copper heat

sinks for example, will require higher penetrating voltage

settings than PBGAs or CBGAs. BGAs with aluminum

heat sinks, on the other hand, do not require the higher

voltages since aluminum is a less dense material and is

therefore much more transparent to X-rays than copper.

7.3.3 Definition and Discussion of X-Ray System Termi-

nology

X-ray inspection systems are available in both

IPC-7095c-7-18

Figure 7-18 Fundamentals of X-Ray Technology

Figure 7-19 X-Ray Example of Missing Solder Balls

Figure 7-20 X-ray Example of Voiding in Solder Ball Con-

tacts

Figure 7-21 Manual X-Ray System Image Quality

IPC-7095C January 2013

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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manual (MXI) and automated (AXI) conﬁgurations. MXI

systems can have varying degrees of automation which can

include automatic BGA analysis, automatic image process-

ing functions, automated manipulation and board handling.

Another feature available with transmission target X-ray

systems is high magniﬁcation using an oblique view (see

7.3.3.2).

What generally distinguishes AXI systems from MXI sys-

tems is that AXI systems are in-line capable and do not

require an operator to make pass/fail decisions. MXI equip-

ment is almost exclusively transmission X-ray technology,

whereas AXI equipment can be transmission, cross-section

and combination.

AXI equipment is generally available in three forms:

• Transmission AX- - commonly referred to as 2-D X-ray

• Cross-Section AX- - commonly referred to as 3-D X-ray

• Combination 2-D/3-D AXI

The following deﬁnitions for Transmission, Cross-section

and Combo Automatic X-ray Inspection apply:

Transmission X-ray automatically generates images of all

features of the sample between the X-ray source and the

detector. Figures 7-23 through 7-25 show examples of

transmission, tomosynthesis, and laminographic X-ray

images.

Cross-section AXI automatically generates images of one

slice of the board at a time. Laminography and tomosyn-

thesis are the most common forms of cross-section AXI.

Combo AXI equipment uses a combination of transmission

and cross-section techniques concurrently during the

inspection of a PCB. Combo systems automatically apply

each technique where it is best suited and allow users the

ability to prefer one technique to another if desired. On

assemblies with components on both sides (Type 2), some

subset of the solder joints will be inaccessible to the stan-

dard transmission X-ray technique due to overlap, unless

an oblique viewing method is utilized.

The cross-section technique on the other hand, will have

greater test access where oblique viewing is not utilized.

Since the transmission X-ray technique captures informa-

tion from the entire solder volume, and the cross-section

technique captures speciﬁc slice information, these

techniques have both unique and common capabilities to

detect some types of solder defects. All of transmission,

cross-section and combo X-ray techniques are capable of

Figure 7-22 Example of X-Ray Pin Cushion Distortion and

Voltage Blooming

Figure 7-23 Transmission image (2D)

Figure 7-24 Tomosynthesis image (3D)

January 2013 IPC-7095C

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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detecting PCB assembly defects that cause changes in the

solder joint proﬁle. These types of assembly defects

include but are not limited to: solder shorts, solder opens,

insufficient solder joints, missing devices, skewed devices,

and solder voids.

7.3.3.1 Transmission X-Ray Technology In transmis-

sion X-ray, the X-ray source and detector can be ﬁxed or

movable in a variety of motions for variations in magniﬁ-

cation and angle of view. Generally, all features in the ver-

tical ‘‘line of sight’’ are viewed concurrently without dis-

tinguishing depth.

Differences in material thickness or density will result in

different transmitted X-ray attenuation at the detector

resulting in brighter or darker intensities within the image

display. For a single material type, such as eutectic solder,

the attenuation of the X-ray photons received at the detec-

tor is proportional to the material thickness. A gray scale

image is created which can be interpreted to determine

whether or not solder joints are acceptable. Figure 7-26

shows a transmission inspection illustration.

7.3.3.2 Oblique Viewing Inspections with Transmission

X-Ray Technology

There are two basic methods of

oblique viewing of objects with transmission X-ray sys-

tems. One method consists of tilting the sample in order to

get the oblique angle as illustrated in Figure 7-27. Although

this method enables the oblique view, the technique may

not allow for the highest achievable level of magniﬁcation

to be realized.

Another method of oblique viewing utilizes a wide angle

transmission X-ray source as illustrated in Figure 7-28. In

this method, the detector rotates around the center axis of

Figure 7-25 Laminographic Cross-Section Image (3D)

Figure 7-26 Transmission Example

IPC-7095c-7-27

Figure 7-27 Oblique Viewing Board Tilt

Oblique Viewing with Board Tilt

Detector

Board with

FBGA

Tilted View

High magnification is

required, but loss of

magnification occurs

through object tilt.

(Due to longer source

object distance.)

IPC-7095c-7-28

Figure 7-28 Oblique Viewing Detector Tilt

Oblique View without

Compromising Available Magnification

Detector

Board with

FBGA

Oblique View

High magnification is

required and maintained by

rotating the detector

through the cone of

radiation while keeping it

perpendicular to the center

of the x-ray source.

(Due to shorter source to

object distance.)

IPC-7095C January 2013

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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