IPC9850_Surface Mount Equipment Characterization.pdf - 第4页

IPC-9850 Official Proposal May 2001 4 inspection systems will improve in their ability to measure component location and orientation. In the future it may become possible to use in-line post-placement (pre-reflow) automa…

IPC-9850

Official Proposal

May 2001

1 Introduction

1.1 Scope

This standard establishes the procedures to characterize machine placement capability of surface mount assembly

equipment in specification documents, as well as in documentation used to verify a specific machine’s placement

capability conformance to the specification, while maintaining a placement accuracy to placement speed

relationship.

1.2 Purpose

IPC-9850 has been developed to standardize the parameters, measurement procedures, and the methodologies used

for the specification, evaluation, and continuing verification of assembly equipment characterization parameters.

These standardized tools shall be used to develop and report the information called out in this standard.

1.3 Background

With the proliferation of Surface Mount Technology (SMT), placement equipment users have struggled with the

question of which machine will perform best in a given manufacturing environment. The advantage of the SMT

assembly process to rapidly place components in precise alignment to the land patterns on the printed wiring board

(PWB) was the initial yardstick by which machines were selected. Machines that could place components the

quickest and with the least amount of scrap were considered the best.

Initially, the most common evaluation method was placement yield. For this evaluation, a machine is made to

populate a large number of the user product where visible placement errors are counted as defects. Machines with

the least defects and the most robust operation were considered best. The high yield and reliability of modern SMT

placement systems require that very large amounts of data be collected to meaningfully assess yield and reliability.

This standard provides new tools for gauging the yield and reliability of placement equipment yet presents

performance results in the traditional metrics.

In addition to the high yield and reliability expected of modern placement equipment, the SMT assembly process

has become significantly more demanding. Components have decreased in size, component terminations are smaller,

and placement locations have moved closer together. All this while the number of components on the PWB and

product volumes have increased significantly. Placement equipment must now place components more rapidly and

with extreme precision to be financially viable. This has made requirements on placement machines more

demanding.

Historically, placement equipment vendors have selected their own parameters and methodologies to present the

specification of their machines’ throughput and placement capabilities. The many representations of this information

have made the comparison between similar types of placement machines very difficult. To obtain comparable data,

users have been forced to conduct on-location evaluations of various machines under the same conditions. This type

of methodology is very time consuming for users and very capital intensive for suppliers.

This standard simplifies the evaluation process by standardizing the performance parameters that describe the

placement machines’ capabilities. It also couples placement throughput and placement quality so speed and accuracy

parameters are dependent on each other. This standard also specifies the methodologies by which the capability

parameters are measured. This reduces potential user-vendor friction created when the user believes the equipment

is not functioning properly. The methodologies specified herein are consistent and verifiable, thus providing

common-ground-methodologies between users and vendors.

These methodologies were achieved by separating machine performance from the rest of the SMT process variables,

which include paste printing, component quality, packaging type and PWB quality. The speed and quality evaluation

methods of this standard specify that measurements will be made by placement of standardized components into

sticky media on clear glass panels. Experience shows that surface mount equipment must perform well on sticky

media before it can perform well in production. Furthermore, improved process capability on sticky tape usually

translates into enhanced process capability in production. Although this method does not provide information that

can be utilized to perfectly predict production quality, this methodology was selected in order to remove as much of

the variation as possible between facilities, products, process, and operators.

While the ultimate goal is to evaluate a machine’s capability to place components in paste on actual PWBs, it is not

currently possible to make such measurements at the required precision and speed. It is anticipated that future in-line

IPC-9850

Official Proposal

May 2001

inspection systems will improve in their ability to measure component location and orientation. In the future it may

become possible to use in-line post-placement (pre-reflow) automatic optical inspection (AOI) systems to measure

the placement machine capabilities.

Due to the convergence of high-speed and fine pitch machines, this standard makes no attempt to separate the two

types of machines. The user is empowered to decide if a particular model is the best solution for the application

based upon the data reported by the supplier.

1.4 Implementation

1.4.1 Characterization Limitations This standard is comprised of a set of parameters that are the lowest common

denominator for surface mount placement equipment. It is be recognized that additional metrics may be of value in

some instances. The collection of parameters selected for this standard comprise the best subset for use as a core set

of requirements to be included with an equipment supplier’s general specification. This core set may change in

future revisions as technology dictates.

In addition, since there are many possible combinations of hardware and software features that are unique to

individual machine types, this standard cannot address every one of them. Such features and options affect the

overall capabilities of specific equipment model and it is left to the user to understand their implications.

Additionally, it is incumbent upon the user to understand the restrictions and leeway provided for each parameter in

this standard so the proper performance conclusions are reached.

1.4.2 Binding Requirements The body of this document is the standard. The word shall is used throughout this

document whenever a requirement is intended to express a provision that is binding. Material in the appendices is

provided only for information and reference.

1.4.3 Test Components Five component types --QFP-100, QFP-208, BGA-228, 1608C capacitor, and SOIC-16 --

were selected to represent the range of component types placed by surface mount equipment. See Table 3-1 and

section 6 for more precise documentation of these component types.

During the verification of a placement machine, one of the goals is to assess the error induced by the placement

machine. To isolate the contribution of the surface mount equipment to the placement error, which is what this

standard intends to hold suppliers accountable for, it is desirable to reduce other effects that may contribute to the

placement error evaluation process. Using nearly perfect components can best reduce the effect of components on

placement error evaluation. Such components minimize the error associated with SMT component-to-component

variation. For instance, 1608C chip capacitors were chosen as test components because the sides of the capacitors

are very precisely and squarely fabricated. Chip resistors were not selected because they are fabricated in a way that

the top edges of the component seen by the vision CMM may not be in good registration with the side or bottom

features of the component used by the placement machines. The electrodes of ceramic chip capacitors are somewhat

problematic because of their bulbous shape.

SOIC-16 integrated circuits were selected as a standard component because of their relatively low cost and sturdy

construction. SOIC-16 components are believed to be representative of a broad class of coarse pitch leaded

components. Almost all SMT placement machines are capable of processing SOIC-16 devices, so this component

makes it possible to compare the performance of the various machine models. Additionally, 1608C Chip capacitors

and SOIC-16s are economically available in tape packaging, which is how most users feed them because it enables

most machines to maximize the placement speed. Both 1608C and SOIC-16 component types must meet the Joint

Electron Device Engineering Council standard (JEDEC Solid State Technology Association, also known as

JEDEC).

Glass slugs are used to present placement machine vision systems with perfect component images that are free of

bent leads and other part imperfections. The glass slugs also allow the inclusion of fiducial markings that the

coordinate measurement machines (CMMs) use to speed up measurements. The slug fiducial markings are measured

by the CMM, instead of the actual slug component features, to represent the location of the slug component feature.

The slug fiducial markings can only be used to represent the position of the slug component feature if the slug has

been United States National Institute of Standards (NIST) certified to that effect. The slug fiducial markings shall

not be processed by the placement machines during the test and are not known to interfere with the normal operation

of the placement machine's vision systems. The clearly defined slug fiducial markings have the benefit of

IPC-9850

Official Proposal

May 2001

minimizing the measurement-induced portion of the total error observed by the measurement machine, and are

particularly important because the specification limits for fine pitch components (QFP and BGA) are so tight.

For this standard, two QFP and one BGA slugs represent component types. Specifically, the QFP-100, QFP-208,

and BGA-228 component types permit the comparison of an extended range of chip-shooters with that of

specialized IC-placers and multi-functional placement systems. To maintain consistency when utilizing slugs, all

slugs in the pickup trays shall have the same orientation.

Other types of SMT components can be studied using the same basic methods defined in the standard. Glass slug

components that represent micro-BGA and Flip-Chips component types are obvious extensions of the standard that

suppliers or users may wish to consider. Rules for adding claims about additional component types are presented

later in this standard.

1.4.4 Test Panels The evaluation methods of this standard specify component placement into sticky media

dispensed on clear glass panels. This approach is advantageous for two reasons. The first is the dimensional stability

of the glass panel, as opposed to epoxy/glass PWB materials that are much more susceptible to shrinking and

wrapping. The second reason is that it permits use of a standard Optical Coordinate Measurement Machine (CMM)

to illuminate the outline of the components. CMMs are able to rapidly measure a large number of components with

very high precision.

In order to streamline the evaluation methodology, a single glass panel type is specified that permits placement

evaluation and verification of a variety of component types. This panel is referred to in this standard as the

Placement Verification Panel (PVP). The PVP has fiducial markings at specified locations with spacing accuracy

traceable to a NIST certification standard. These fiducials are used as references by both the placement and

measurement machines.

The panels accommodate the following component groups (one component group at a time) for this standard:

a. 36 QFP-100,

b. 30 QFP-208

c. 100 BGA-228

d. 80 SOIC16

e. 400 1608C (Capacitors)

Application of the sticky media requires experience. There must be sufficient amount of sticky media to hold the

component in place, but not too much as to cause interference with the back light intensity. Appendix C has

guidelines on the application of the sticky media.

1.4.5 Measurement This standard has been developed with emphasis on assuring that the measurement tools are

capable of properly characterizing the process. Capable measurement tools provide the customer with a

methodology for verifying vendor claims. They also assure the vendor that the customer is properly evaluating the

machine performance. For an Optical CMM to be a capable gauge for evaluating the surface mount process, its

accuracy and repeatability must be significantly higher that the accuracy and repeatability of the surface mount

equipment. The measurement capabilities required by the CMM depend on the type of components being evaluated

and on the specification limits that the supplier is committing to.

The accepted method for evaluating measurement system performance is called Gauge Repeatability and

Reproducibility (GR&R). This methodology determines the measurement system’s ability to consistently measure

the same product over and over again. The methodology requires that the measurement uncertainty (6x the GR&R

error) be at most 25% of the specification range of the product being measured. GR&R studies do not assess the

accuracy of the measurements, just their consistency. An additional check is needed to verify that the CMM

measurement routine is producing accurate results. See Appendix G for discussion.

The accuracy of the Optical CMM can only be evaluated against a certified gauge. The gauge selected for this

standard is a NIST traceable glass verification panel with etched images in the shapes of the selected components.

This panel is measured on the CMM, and the reported positions are compared to the actual positions of the

component images provided from the panel certification.