IPC-D-279 EN.pdf - 第120页

Appendix K Design for Manufacturability and Assembly Checklist K-1.0 SUMMARY Deﬁnition of manufacturability: a measure of the ease or simplicity with which a product can be manufactured or assembled. These guidelines dea…

can also be used as a process control measure once the

process is under control.

J-8.0 ISSUES AND CONCERNS OF TESTING

J-8.1 Test Equipment

The tester used with certain high-

density assembly technologies may itself have limitations

which must be considered. As single line conductor pitch

continues to fall, it becomes increasingly difficult to probe

all points, even if they are located on an outer layer. Probe

points on the test head become increasingly fragile. Copla-

narity of the test head and assembly is also a concern.

J-8.2 Test Points The distribution of test points routed

on or brought to an outside layer is also an issue. If they

are clustered together, too much pressure may be brought

to bear on a small area of fragile substrate. In particular,

dense circuits may have difficulty placing test points for all

desired nodes on an outside layer.

J-8.3 Costs Cost issues also need to be considered.

Reducing the test probe grid below 1.25 mm results in

more expensive test ﬁxtures. Test probes with these spac-

ings are quite fragile and may require frequent placement.

Clam shell ﬁxtures, which can simultaneously probe both

sides of an assembly, if required, are also costly. In addi-

tion, clam shell ﬁxtures may be subject to timing problems

since back side wires in the test ﬁxtures may be longer than

front side ones.

J-8.4 CAD/CAE Software A host of issues are associated

with the hardware and software platform on which CAD/

CAE software runs. They are beyond the scope of this

document. However, suffice it to say that CAD/CAE soft-

ware vendors must be attentive to the changing trends in

technologies; even with a large installed base, proprietary

platforms are already proving to be obsolete.

IPC-D-279 July 1996

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Appendix K

Design for Manufacturability and Assembly Checklist

K-1.0 SUMMARY

Deﬁnition of manufacturability: a measure of the ease or

simplicity with which a product can be manufactured or

assembled.

These guidelines deal with Design for Manufacturability

(DfM) primarily at the detailed component and process

levels and the focus is on doing things right, particularly

with respect to improving quality and reliability; if the

DfM process is used early in the design process, the focus

can be on doing the right things in terms of system organi-

zation and setting testability expectations. More beneﬁts

are derived from early use of conceptual design and DfM

processes.

Section Topics:

• Minimize number of parts

• Minimize number of part numbers

• Design for robustness (Design of Experiments)

• Eliminate adjustments

• Design for efficient and adequate inspection and test-

ing (testability)

• Eliminate engineering changes on released products

• Make assembly easy and foolproof (Poka-Yoke)

• Use repeatable, well-understood processes

• Choose parts that can survive (are compatible with)

process operations including rework, repair and main-

tenance

• Choose or design process for compatibility with sus-

ceptible parts

• Layout parts for reliable process completion

Table K-1 Checklist for Design for Manufacturability and Assembly

GUIDELINE AREA OF QUALITY/RELIABILITY IMPROVEMENT

Minimize Number of Parts

Fewer part and assembly drawings

Less complicated assemblies

Fewer parts to hold to required quality characteristics

Fewer parts to drift or fail

Fewer solder attachments to make or fail

‘Design Guidelines for Quality Improvement’

Fewer documents to control

Lower assembly error rate

Higher consistency of part quality

Higher reliability

Minimize Number of Parts

Fewer variations of like parts Lower assembly error rate

Design for Robustness (Design of Experiments)

Low sensitivity to component variability

PTH, via aspect ratio (AR) < 5:1 temperature

or use blind/buried vias

Use standard or preferred parts (EIA/JEDEC registered)

Use compatible SM land patterns (IPC-SM-782)

Higher ﬁrst-pass yield and less degradation of

performance over time

Less sensitivity to cycling and thermal shock, lower failure rate

Fewer new failure modes and mechanisms

Fewer suppliers to manage

Widen process window

Increase assembly yield

Eliminate Adjustments

No assembly adjustment errors

Eliminate adjustable components with high failure rates

Eliminate change in adjustments under vibration and shock

Provide adjustments and compensation through software

Consider digitally switched resistor network

Higher ﬁrst-pass yield

Lower failure rate

Design for Efficient and Adequate Inspection and Testing (Testability)

Less mistaking ‘‘good’’ for ‘‘bad’’ product and vice versa

Less effort to locate defects

Better control over rework/repair

Truer assessment of quality, less unnecessary rework

Faster diagnosis to root cause

Less service/maintenance time

More ‘‘up’’ time

Less part damage

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GUIDELINE AREA OF QUALITY/RELIABILITY IMPROVEMENT

Eliminate Engineering Changes on Released Products

Fewer errors due to changeovers & multiple revisions/versions Lower assembly error rate

Make Assembly Easy and Foolproof (Poka-Yoke)

No ‘‘force ﬁtting’’ of parts

Parts cannot be assembled wrong

Obvious when parts are missing or wrong orientation

Assembly tooling designed into part (self-aligning/securing)

Less damage to parts, faster and better serviceability

Lower assembly error rate

Use Repeatable, Well-Understood Processes

Part quality easy to control

Assembly quality easy to control

Higher part yield

Higher assembly yield

Choose Parts that Can Survive (are Compatible with) Process Operations including Rework, Repair and Maintenance

Less damage to parts

Less part degradation or latent damage through prior

evaluation

Plastic Encapsulated Surface Mount Components -

IPC-SM-786

SM Connectors - IPC-C-408

Other SM Components - IPC’s ‘‘Solvent Compatibility’’

No silver termination ﬁnish

No nickel termination ﬁnish

No thick gold printed board or termination

Minimize number of TH components

Maximize printed board Tg (glass transition temperature)

Printed board thickness compatible with placement machine

Dry ﬁlm solder mask and solder paste compatibility

Components and solder mask result in adequate clearance

to printed board

Higher yield

Higher reliability

Avoid silver leaching, weak solder joint

Increase solderability, joint strength

Increase solder joint visual yield ﬁnish

Lower defects due to solder bridging wider TH and

SM process latitude

Decrease hand loading, manual soldering

Decrease patent and latent printed board damage at high

process temperatures

Minimize solder balls

Enhanced cleaning. Higher SIR PWA robust to dendrite

formation

Choose or Design Process for Compatibility with Susceptible Parts

Less part damage or degradation

Ceramic components thermal shock < 4°C/second

Sensitive components preheated so that ∆T < 100°C

Susceptible Plastic Encapsulated Surface Mount Components

handled per IPC-SM-786

Don’t impact ceramic parts with pick and place tooling

Reﬂow process adjusted for thermal unbalance due to

thermal masses of parts (PGA, Heat Sinks)

Dry susceptible substrates before reﬂow

Component terminations not used for in-circuit testing

Higher yield

Higher reliability

Layout Parts for Reliable Process Completion

Less damage to parts during handling and assembly

Orient parts for non-interfering single axis insertion

Sequence parts for insertion for easy disassembly

Orient similar parts similarly

Parts not hanging over solder quality (own or neighboring

parts). No shadowing

Parts can automatically be placed or inserted

Higher yield, higher reliability

Less part damage

Easier rework, repair and maintenance

Fewer orientation sensitive bridging or solder joint failure

modes

Consistent solder joint

Lower assembly error rate

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