IPC-7095C-2013.pdf - 第36页

4.3.5 Package-on-Package BGA The package-on- package (PoP) innovations are proving to be preferred for a broad range of SiP applications. User companies have realized that complex mixed-technology functions can be produc…

Although not mandatory, nonsymmetrical ball patterns

have the added advantage of enabling automated orienta-

tion detection during assembly. One example is to omit one

of the corner balls in an otherwise symmetrical array.

4.3.2.1 Future Ball Contact Size Conditions Although

not required for the BGAs shown in Table 4-2, future ball

sizes contemplated are shown in Table 4-3.

4.3.2.2 Land Pattern Approximation The land pattern of

the component substrate (where the ball is attached) and

the land pattern of the mounting structure (printed board)

should be as similar in diameter as possible. Component

manufacturers have determined that the printed board land

pattern or the pad on the component should be slightly less

than the ball diameter. The amount of reduction is based on

the original ball size, which is used to determine the aver-

age land. In determining the relationship between nominal

characteristics, a manufacturing allowance for land size has

been determined to be 0.1 mm between the maximum

material condition (MMC) and least material condition

(LMC) for ball diameters of 0.40 mm and above and less

for balls that are smaller.

The information shown in Table 4-4 provides data on land

patterns and their variation to accommodate nine ball

diameters.

Many component manufacturers use solder mask-deﬁned

lands (see 6.2.2). When this technique is employed, the

nominal land diameter should be increased by the amount

of solder mask encroachment on the land (usually about

0.1 mm). The opening in the solder mask window then

represents the diameter to which the ball will become

attached, while the actual land is slightly larger to accom-

modate the solder mask-deﬁned land concepts. It should be

noted that routing density is decreased, since the land is

larger.

4.3.3 BGA Package Outline Body sizes for ball grid

arrays are divided up into the following two outline groups:

square and rectangular. The square outline package family

size ranges from as small as 4 mm x 4 mm and as large as

50 mm x 50 mm. In the ﬁne pitch variations, the package

sizes increase in 1.0 mm increments. In the ranges above

21 mm x 21 mm, the body size increases in increments of

2.0 mm to 2.5 mm and the pitches are in the regular range.

Rarely will any of the ﬁne pitch parts be found in sizes

larger than 21 mm x 21 mm. The rectangular BGA family

has the same size ranges from 4.0 mm to 50 mm but varies

by each application. This group can have many more varia-

tions than the square group. Rectangular sizes typically are

found to follow no ﬁxed incremental progression. This

group is normally driven by the memory applications and

closely follows the die sizes. Rectangular sizes are nor-

mally standardized in small application speciﬁc families.

The ﬁne pitch BGA components, equal to or less than 0.8

mm, rarely exceed 21 mm in body size.

A ﬁne pitch ball grid array (FBGA) is a 0.50 to 0.80 mm

pitch solder balled array package that have ﬁxed package

dimensions ‘‘D (Length)’’ and ‘‘E (Width).’’ The FBGA is

more like the plastic and ceramic BGA families described

above having ﬁxed body dimensions. Although the FBGA

outline is typically only 20% larger than the die, it will not

change shape with every die shrink.

The die-size ball grid array package (DSBGA) is a 0.30 to

0.50 mm pitch solder balled array package that has variable

package dimensions ‘‘D (Length)’’ and ‘‘E (Width).’’ The

DSBGA package takes the shape of the die which normally

makes it a rectangular outline and is presently widely used

in Flash and DRAM Memory devices. The rectangular die

size (RDS) outline will likely change ‘‘D’’ and ‘‘E’’ dimen-

sions with every die shrink.

4.3.4 Ball Size Relationships The total variation of the

system considers three major issues: positioning, ball toler-

ance, and substrate tolerance. All three attributes added

together result in a worst case analysis; however, as with

other land patterns in the standard, a statistical average is

determined by using the RMS (root mean, square) value.

The trend toward higher pin-count ICs and smaller package

outlines has enabled companies to improve both product

functionality and performance. Table 4-5 will assist the

user in calculating variations in land pattern geometry for a

wide range of BGA applications, and shows the total varia-

tion in the system for each of the nine ball sizes identiﬁed

in the standards. As noted, the standard nominal dimension

for ball contact diameters are 0.15, 0.20, 0.25, 0.30, 0.40,

0.45, 0.50, 0.60, and 0.75 mm. Ball contact size for array

packages are inﬂuenced by the limit established for overall

package height, ball contact pitch and the desire to maxi-

mize solder joint reliability.

Table 4-3 Future Ball Size Diameters for DSPBGAs

Nominal Ball

Diameter (mm)

Tolerance

Variation (mm) Pitch (mm)

0.25 0.28 - 0.22 0.40

0.20 0.22 - 0.18 0.30

0.15 0.17 - 0.13 0.25

Table 4-4 Land Size Approximation

Nominal Ball

Diameter (mm) Reduction

Nominal Land

Diameter (mm)

Land

Variation (mm)

0.75 25% 0.55 0.60 - 0.50

0.60 25% 0.45 0.50 - 0.40

0.50 20% 0.40 0.45 - 0.35

0.45 20% 0.35 0.40 - 0.30

0.40 20% 0.30 0.35 - 0.25

0.30 20% 0.25 0.25 - 0.20

0.25 20% 0.20 0.20 - 0.17

0.20 15% 0.15 0.15 - 0.12

0.15 15% 0.10 0.10 - 0.08

January 2013 IPC-7095C

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--`,,```,,,,````-`-`,,`,,`,`,,`---

4.3.5 Package-on-Package BGA The package-on-

package (PoP) innovations are proving to be preferred for

a broad range of SiP applications. User companies have

realized that complex mixed-technology functions can be

produced with higher yield and more economically if the

semiconductors are individually prepackaged and tested

before joining. The most common solution for PoP appli-

cations utilizes package sections designed around the exist-

ing JEDEC FBGA standard array packaging format (see

Figure 4-5). Stacking prepackaged die has less risk because

the individual packages are fully tested before conversion

to the stacked PoP format.

Whether or not to join one package to the other before or

during the board level assembly process is a decision that

may be inﬂuenced by the requirement for in-process con-

ﬁguration ﬂexibility. For example, the base package can be

furnished by vendor ‘‘A’’ while the memory sections of the

stack are supplied by vendor ‘‘B,’’ ‘‘C’’ or ‘‘D.’’ After all,

memory functions are available from a greater number of

sources and the testing for memory is somewhat special-

ized. Furthermore, the concern of ownership of total qual-

ity and reliability can be alleviated. The logic device sup-

plier is responsible for the logic, the memory

manufacturers are responsible for the respective memory,

and the board assembler is responsible for only the surface

mount attachment of the two. This alternative has two ben-

eﬁts. It allows the user to specify multiple variations (dif-

ferent memory functions, data rate and so on) as well as

accommodating secondary sources of supply.

4.3.6 Coplanarity A critical issue in surface mount

packages is the limits for coplanarity of the contacts. The

coplanarity requirements in a BGA package are very differ-

ent from other lead-frame packaged surface mount compo-

nents. Coplanarity for any BGA is the distance of compo-

nent contact surface above a common seating plane. Thus

noncoplanarity, a simpliﬁed term, is the maximum distance

between the lowest and the highest contact when the pack-

age rests on a perfectly ﬂat surface. This deﬁnition repre-

sents a package sitting on a PC board on at least three

locations.

Coplanarity tolerance deﬁnes the distance from the seating

plane to the highest point of the package. This dimension

includes the standoff height, package body thickness and

(if present) lid thickness. The measurement criteria do not

include attached features such as heat sinks or other com-

ponents. An integral heat-slug, however, is not considered

an attached feature. If the package happens to be laminate

substrate based BGA, additional coplanarity issues can be

expected due to problems associated with adapting larger

substrates and maintaining ﬂatness within the tolerances.

This, in part, is the reason why the plastic BGA (PBGA)

package coplanarity requirement is established at 150 µm.

Most suppliers would like the allowable BGA coplanarity

limit to be around 200 µm but the users would prefer the

maximum to be no greater than 100 µm (see 4.6.2.6 and

4.8.4). There are different coplanarity requirements for dif-

ferent types of BGAs. Table 4-6 shows a sampling of

JEDEC registered BGA package outlines.

The coplanarity values may vary from JEDEC outline-to-

outline because of the ball metallurgy. In low temperature,

eutectic (183°C melting point) solder balls, the balls

Table 4-5 Land-to-Ball Calculations for Current and Future BGA Packages (mm)

Land Size

Location

Allowance

Ball

Variation

Ball Size

% Reduction

from Nom.

Variation

AllowanceMMC LMC Nominal MMC LMC

0.60 0.50 0.10 0.25 0.75 0.90 0.65 25% 0.25

0.50 0.40 0.10 0.20 0.60 0.70 0.50 25% 0.20

0.45 0.35 0.10 0.10 0.50 0.55 0.45 20% 0.17

0.40 0.30 0.10 0.10 0.45 0.50 0.40 20% 0.17

0.35 0.25 0.10 0.10 0.40 0.45 0.35 20% 0.17

0.25 0.20 0.05 0.10 0.30 0.35 0.25 20% 0.15

0.20 0.17 0.05 0.06 0.25 0.28 0.22 20% 0.08

0.15 0.12 0.05 0.04 0.20 0.22 0.18 15% 0.07

0.10 0.08 0.05 0.04 0.15 0.17 0.13 15% 0.07

IPC-7095c-4-5

Figure 4-5 JEDEC Standard Format for Package-on-

Package Components Source: JEDEC Publication 95-4.22

= 0.65 mm

0.50 mm

0.65 mm

0.80 mm

0.50 mm

Table 4-6 Examples of JEDEC Registered BGA Outlines

Registered Outline Package Type Coplanarity

MO-151 Plastic BGA 0.20 mm

MO-156/MO-157 Ceramic BGA 0.15 mm

MO-195 Fine Pitch BGA 0.08 mm

IPC-7095C January 2013

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--`,,```,,,,````-`-`,,`,,`,`,,`---

collapse during the assembly operation; therefore, the

coplanarity requirement is not as tight as a high tempera-

ture (302°C melting point) solder balls in which the balls

do not collapse during the assembly operation.

4.4 Component Packaging Style Considerations The

JEDEC Design Guidelines for BGA do not deﬁne speciﬁc

materials or method of assembly. The base material will

vary from one supplier to another depending on applica-

tion. The base structure is most likely a reinforced organic

laminate, a nonreinforced polyimide ﬁlm or ceramic.

Ceramic-based BGA packages are often supplied with non-

collapsing solder balls made of high temperature solder

(90% lead, 10% tin) with a melting point of 302°C. The

ball size will vary with the pitch and package size. Larger

packages will usually have larger ball sizes to improve

reliability. Since the ceramic package is relatively very ﬂat

and the tolerances in ball diameters are very narrow, the

coplanarity requirements can be relatively narrow as well.

The supplier of the ceramic-based package will generally

furnish recommendations for selecting a suitable solder

paste composition for board level assembly.

In an effort to develop new attachment methods, a patent

was ﬁled in the late 1990’s that uses a polymer-coated ball

as the interconnection media. The metallic sphere is con-

ductive and may be made of copper, silver, gold, solder,

etc. and then coated with the conductive polymer. The

method of coating is left up to the ball producer and may

be of different thickness as required for the application.

This novel interconnect method was developed in order to

address the different CTE of a ceramic interposer and the

organic board. Several technical papers have been pub-

lished on the system that heats the interfaces and how the

conductive polymer joins the land on the interposer and the

board. Temperature cycling data was obtained from both

conventional and polymer core balls tested on ceramic

packages mounted on an FR-4 board. An electrical simula-

tion was also performed to compare the polymer-core ball

with a conventional solder ball. Figure 4-6 shows the con-

cept of the process.

Laminate and polyimide ﬁlm-based BGAs are very differ-

ent, however. The laminate based package is essentially

made of circuit board material with a high temperature (T

)

rating. A high T

rated resin system adopted by several

companies for BGA package applications is bismaleimide

triazine (BT). Reinforced polyimides and polyimide ﬁlms

have an even higher temperature rating and are also in

wide use for both BGAs and FBGAs.

4.4.1 Solder Ball Alloy Solder ball composition is

deﬁned by the overall PCA technology, e.g., tin/lead or

lead-free, and the package type, e.g., ceramic or laminate

substrate. The alloy composition selected for ball contacts

on reinforced laminate and polyimide ﬁlm based BGA

packages can vary a great deal. Many are furnished with a

tin/lead eutectic solder having a melting (liquidus) point of

183°C (or 179°C for eutectic solder with 2% silver). The

ball contacts are commonly applied to the package sub-

strate using only ﬂux and a reﬂow soldering temperature of

215-220°C to complete the joining process.

4.4.1.1 Tin/Lead Technology Alloys Although not in

wide use for most commercial applications, tin/lead alloys

can be adapted for both solder ball and solder joining mate-

rials. One common alloy composition is the Sn63Pb37

eutectic, with a liquidus temperature of 183°C. The eutec-

tic silver containing alloy composition, Sn62Pn36Ag2, has

a liquidus temperature of 179°C and is an acceptable alter-

native to eutectic Sn63Pb37. Ceramic BGAs, when used in

the tin/lead technology, often employ a high-lead alloy of

Sn10Pb90 composition to provide the required solder joint

reliability. This alloy does not melt during the tin/lead

reﬂow process, but when attached to the PCB with eutectic

Sn63Pb37, provides a reliable interconnect.

4.4.1.2 Lead-free Technology Alloys In compliance

with the RoHS directive (Restriction of the Use of Certain

Hazardous Substances in Electrical and Electronic Equip-

ment), companies manufacturing electrical and electronic

assemblies and electrical components must use Pb-free

(lead free) materials for both ball contacts and package to

substrate joining. Although a number of Pb-free alloy

compositions are available, a majority of manufacturers

have adopted tin as the primary element and include

silver or a combination of silver and copper to the tin

alloy. Typical Pb-Free alloy compositions include

Sn96.5Ag3.0Cu0.5 (SAC305), Sn95.5Ag3.8Cu0.7

(SAC387) or Sn95.5Ag4.0Cu0.5 (SAC405). These solders

have liquidus temperatures in the range of 217-227°C and

IPC-7095c-4-6

Figure 4-6 Polymer Coated Sphere Interconnection

Copper

Land

Solder

Mask

Package

Substrate

Interconnection

Substrate

Copper

Land

Polymer

Core

Solder

January 2013 IPC-7095C

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--`,,```,,,,````-`-`,,`,,`,`,,`---