IPC-7095C-2013.pdf - 第89页

the processes, and the shop-ﬂoor equipment. Applications receiving messages from the equipment include: • W ork-in-process (WIP) • T racking, capacity , and throughput monitors • Equipment utilization and line-balancing …

board thickness, etc. The test plots should be employed to

verify that the data matches the requirements.

Other documentation may include numerical control data

for drilling, routing, libraries, tests, artwork, and special

tooling. There are design and documentation features/

requirements that apply to the basic layout, the production

master (artwork), the mounting structure itself, and the end

item component or printed board assembly. All must be

taken into consideration during the design of the mounting

structures for the bare die, or the mounting structure for the

BGA. Documentation shall meet the requirements of IPC-

2611. In order to provide the best documentation package

possible, it is important to review IPC-2611 and identify all

the criteria that are affected by the design process.

6.8.1 Drawing Requirements During the formal design

review prior to layout, special tools that can be generated

by the design area in the form of artwork or numerical

control data shall be considered. This tooling may be

needed by fabrication, assembly, or testing. Examples of

such tooling are drilling data ﬁles, solder paste stencils,

data for component placement, ICT ﬁxture data, and art-

work in the form of layered graphics, silk screen and sol-

der mask.

When viewing the documentation, it is always viewed from

the primary side. All phototool generation is viewed from

that same direction. The deﬁnition of layers of the product

shall be viewed looking through the particular part from

the primary side.

Accuracy and skill must be sufficient to eliminate misinter-

pretation during the artwork generation process. This

requirement can be minimized by adhering to a grid or

pitch of the component terminations, which drive so many

features on the board or the bare die.

Layout notes should be as complete as possible with the

addition of appropriate notations. Marking requirements

and revision status level deﬁnition are key to maintaining

conﬁguration management conditions. It is especially

important for the engineering review cycle, a quoting

effort, and when the document is used by someone other

than the originator.

6.8.2 Equipment Messaging Protocols Throughout the

electronics industry manufacturing consists of numerous

steps, each of which often centers around one supplier’s

equipment. Although the steps are generally well-

automated within themselves, they are only peripherally

connected to one another. Proprietary data formats and

communications protocols prevent the islands of automa-

tion from talking to one another. This condition also pre-

vents factory managers from monitoring, understanding,

and possibly correcting the manufacturing process to

improve throughput and product quality.

In the last few years, building on an International Electron-

ics Manufacturing Initiative (iNEMI) funded project, the

IPC has standardized data syntax and semantics in elec-

tronics assembly, establishing rules for data exchange both

on a single factory ﬂoor and between that ﬂoor and the rest

of a manufacturing organization. The results have been

published as the IPC CAMX (computer-aided manufactur-

ing using the extensible markup language [XML]) stan-

dards: The standards are:

• IPC-2541, Generic Requirements for Electronics Manu-

facturing Shop-Floor Equipment Communication

• IPC-2546, Sectional Requirements for Shop-Floor Equip-

ment Communication Messages (CAMX) for Printed Cir-

cuit Board Assembly

• IPC-2547, Sectional Requirements for Shop Floor Equip-

ment Communication Messages (CAMX) for Printed Cir-

cuit Board Test, Inspection and Rework

At the heart of the standard is a framework with an inter-

mediary. This is the ‘‘message broker’’ that handles infor-

mation exchange and complies with the IPC-2501 Standard

(‘‘Deﬁnition for Web-based Exchange of XML Data’’). The

message broker can be thought of as a post office or a mail

server. Messages are sent to the server and, when the infor-

mation is needed, it is asked for by the equipment or the

manager who wants the data.

In a factory, several lines of equipment and several appli-

cations may connect to the message broker at the same

time. Individual elements need not know any details about

the nature, conﬁguration, or format of the others. They

communicate directly only with the broker. When people

and equipment need speciﬁc information, the broker pro-

vides it in the correct format.

6.8.2.1 Implementation It is relatively easy to set up the

infrastructure and web-based tools to monitor several sets

of manufacturing equipment, including in-circuit testers,

and several suppliers’ pick-and-place machines. The setup

can be used to gathered performance and functional feed-

back data on the message broker. The message broker can

usually be up and running in two days, being able to con-

nect reasonably easily with both legacy equipment and any

XML-ready equipment using an infrastructure that is in

place at the manufacturing site. In a careful installation, it

is also possible to avoid compromising network security

requirements.

Using internet standards like HTTP and XML ensures the

interoperability between different platforms. Although an

application has never been run against a running message

broker before, it can be adapted to the existing communi-

cation framework on site. One important goal of the IPC-

CAMX standards is to lower the technological barrier to

ease the integration of sophisticated equipment like pick-

and-place machines and test equipment, as well as simpler

equipment like printed board handlers. The CAMX stan-

dards provide data about the products under manufacture,

IPC-7095C January 2013

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the processes, and the shop-ﬂoor equipment. Applications

receiving messages from the equipment include:

• Work-in-process (WIP)

• Tracking, capacity, and throughput monitors

• Equipment utilization and line-balancing monitors

• Product quality monitors that incorporated data from test

and inspection

Linking all parts of a manufacturing operation through a

single hub has been the goal for many years. The CAMX

message-broker approach provides an extraordinary array

of tools to accomplish that task. The message broker can

connect any number of clients together. Clients can be fac-

tory equipment, a host computer, or the data hub at the

engineering manager’s desk. The system provides visual

representation of whatever the manager wants to know. The

manager can communicate with someone in Singapore, and

check the status of their work-in-process using a snapshot

of the data in any of a number of preset formats. He can

pick the format and instruct the software as to how fre-

quently the updates are required, and the broker does the

rest.

6.8.2.2 Information Exchange Benefits Major equip-

ment manufacturers have involved themselves in this effort

from the beginning, thus they support the CAMX effort to

extract information from their machines in the standard

format. Critical to the success of this new tool is its ‘‘plug-

and-play’’ construction. Any piece of equipment on the

ﬂoor can connect to the supporting architecture and data-

gathering software. Using XML as the standard ensures

that no one will misinterpret what the data means. Process

correction and product improvement require traceability of

faults, regardless of where a fault is identiﬁed. Knowing

where the fault came from and its root cause are critical.

In addition, increasing product quality and reducing costs

require understanding the actual fault spectrum. Histori-

cally, the same fault may be called by several names at dif-

ferent process points. Applying the CAMX standard, fault

names can be consistent from step to step within the manu-

facturing operation, thereby improving the overall level of

communication.

For electronics manufacturing service (EMS) providers, the

CAMX standards permit manufacturing ﬂexibility without

sacriﬁcing data coherence and comprehensive data analy-

sis, regardless of the process under evaluation. The soft-

ware is more streamlined and less complex than systems

that were developed for the semiconductor industry

because all of the equipment now conforms to the single

standard. The result is equipment that is both easier to use

and easier to support.

Standardization will open up opportunities to perform more

elaborate data analysis because the standards will reduce

the effort required to gather information. IPC-2501, as

implemented in the CAMX message broker, provides the

simpliﬁed web-based XML messaging activity for the other

IPC standard vocabularies. Equipment suppliers who need

a particular piece of information will merely ‘‘subscribe’’

to an application or system using the existing Web-based

and universal XML messaging SOAP protocol, regardless

of the architecture of the other interfaces, and download

responses in real time. SOAP is an XML messaging stan-

dard supported by all major computing and software

vendors. It forms the foundation of their Web-services

infrastructures.

The XML message type of machine communication was

less necessary when OEMs did their own manufacturing.

However, with the amount of outsourcing that kind of ver-

tical integration has become more the exception than the

rule. The new standards will make it possible for the OEM

customer to regain a measure of the insight into manufac-

turing activity that was lost due to outsourcing the work.

The use of a universal data format will also provide the

ability of suppliers to monitor inventory of their products

to prevent disruptions of the manufacturing line. Compo-

nent suppliers can monitor usage of their components on

the factory ﬂoor, scheduling purchases and taking over

similar functions that otherwise fall to the EMS company

or to the OEM.

6.8.3 Specifications In many instances, documentation

references other speciﬁcations. These should be clear and

should be provided in this same manner in which the origi-

nal package is provided (hard copy or electronic). Confor-

mance test circuitry shall be provided, thus the part can be

tested through destructive techniques. As a minimum, con-

formance test circuitry shall include:

• Board part number/revision letter

• Assembly part number and reference to Bill of Material

• Traceability identiﬁcation

• Date code

• Manufacturer’s identiﬁcation, e.g., commercial and gov-

ernment entity (CAGE), logo, etc.

• Special coding systems may be used provided they are

identiﬁed on the master drawing

January 2013 IPC-7095C

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7 ASSEMBLY OF BGAS ON PRINTED CIRCUIT BOARDS

7.1 SMT Assembly Processes

The assembly processes

for attaching BGA components are more forgiving than the

processes for attaching ﬁne pitch peripheral components in

some aspects, but more demanding in others. Process

defect rates are signiﬁcantly less than ﬁne pitch peripheral

components; however, good process control is a necessity.

7.1.1 Solder Paste and Its Application The surface

mount assembly process uses solder paste to connect the

BGA balls to the lands on the board. Solder paste can be

applied to the lands using three methods: screening, sten-

ciling, and dispensing. BGAs are typically printed using

stenciling where solder paste is applied on the BGA lands

through the apertures on the stencil of similar size or

smaller to the BGA lands.

Stencil thickness and aperture size will determine the

designed paste volume, which can be critical for the solder

joint reliability of certain BGA types. Squeegee type and

process settings will impact the actual solder paste that is

deposited. The stencil thickness may need to be reduced

when using ﬁner pitch BGA components; however, care

needs to be taken when reducing stencil thickness so that

volume is not reduced for other components. Trapezoidal

stencil apertures (slightly larger opening on the bottom

than on the top) are generally preferred as they improve

paste release.

Solder paste consists of a homogeneous mixture of metal

powder particles and ﬂux. The metal content (typically

90% by weight) in the solder paste determines the amount

of solder in the solder joint. The most common solder paste

alloy is the eutectic Sn63Pb37, and SAC 305 for lead-free

(Sn96.5Ag3.0Cu0.5). Metal powder particles are generally

spherical in shape. A uniform shape aids the printing or

dispensing process and it decreases the surface area, which

minimizes oxidation.

Flux makes up the majority of the remaining substances in

the solder paste. The activators in the ﬂux remove oxides

from the solder particles, the land, and the BGA balls. They

promote good solderability during reﬂow process. Solder

balls, which form for a variety of reasons during reﬂow, are

a reliability concern, especially when ﬁne pitch devices are

involved. The solvents have an important role in control-

ling the tackiness of the paste and affecting the rheological

properties. The formation of voids in the BGA solder joint

may be related to solvents in the solder paste. Solvents

with low boiling points and/or improper reﬂow parameters

can increase the incidence of voids in BGA solder joints.

For successful ﬁne pitch BGA printing, the solder paste

must pass through very small apertures in the stencil. The

solder paste needs to remain printable and tacky for an

extended period of time, and it must maintain print deﬁni-

tion prior to and during reﬂow. Solder paste viscosity, par-

ticle size and stencil life are critical parameters for solder

paste application.

7.1.1.1 Particle Size and Paste Selection Many solder

pastes are available and one should be selected based on

(among other things) the print characteristics, ﬂux type,

and ﬁne pitch particle size. Print characteristics includes

that the solder paste print well, providing good print deﬁ-

nition without exhibiting solder paste slump. The ﬂux in

the paste should be active enough to exhibit good wetting

and reﬂow characteristics, yet it should be compatible with

the cleaning process or surface resistivity requirements if a

no-clean ﬂux is used. The diameter of the particle size

should not exceed the aperture width divided by 4.2. This

was determined through empirical experimentation. When

this rule is violated, the paste release and print deﬁnitions

are affected.

The solder particle size is classiﬁed by J-STD-005 (see

Table 7-1).

Particle size distribution affects the solder paste viscosity

and printability. Type 3 paste is the most commonly used,

and it is adequate for most printing applications. Ultra ﬁne

pitch CSP application may require Type 4 paste. Care

should be taken when moving to Type 4 powder as the sol-

derability is generally reduced due to the increase in the

surface area and the potential for increased oxidation of the

solder particles. It is often necessary to use nitrogen in the

reﬂow furnace when Type 4 powders are incorporated.

7.1.1.2 Stencil Thickness and Aperture Design As is

the case for all components, as the pitch of the part

decreases it often becomes necessary to decrease the sten-

cil thickness. For BGA components in the pitch range of

1.5 mm to 1.0 mm, a stencil can range from 0.15 mm

[0.006 in] to 0.18 mm [0.007 in] thick. For chip scale

packages (CSP) or ﬁne pitch BGAs with a pitch ≤0.80 mm,

a stencil thickness range of 0.1 mm [0.004 in] to 0.15

[0.006 in] mm is recommended. CSPs and other ﬁne pitch

area array packages are seldom the only components on a

PCA so a balance must be struck in the selection of stencil

thickness. Thin stencils, appropriate for optimal CSP print-

ing, will likely not provide sufficient solder paste for other,

larger pitch BGAs. This can lead to defects such as head-

in-pillow or reduce the thermal fatigue life of critical

ASICs.

Table 7-1 Particle Size Comparisons

Solder Paste Type Mesh

Maximum Particle

Size [µm]

Type 2 -200/+325 75

Type 3 -325/+500 53

Type 4 -400/+500 38

Type 5 -500 25

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Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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