IPC-D-859.pdf - 第45页

Sometimes this interconnection uses pins, where a pin passes through the substrate and the ﬂex cable to provided the proper interconnection. At other times, the ﬂex cable may be surface soldered directly to land patterns…

depends on the application. However, these parameters

should be clearly deﬁned on the procurement document for

these parts.

For optimum board design efficiency, the bus bar terminals

should interface with the circuit on a uniform termination

pattern.

4.6.3 Flex Cable When ﬂexible cable becomes part of a

hybrid circuit assembly the terminations shall be accom-

plished in the manner that imposes no undue stress on the

cable/assembly interconnection.

IPC-859-4-11

Figure 4–11 Modiﬁed fan-out patterns

IPC-859-4-12

Figure 4–12 Leadless discrete components

▼

B. Reflow ConfigurationA. End Cap Configuration

A B

Reflow

Terminal

Area

End

Cap

▼

IPC-859-4-13

Figure 4–13 Improper mounting of end-cap discrete

components

IPC-859-4-14

Figure 4–14 Chip resistor with deposited element

IPC-D-859 December 1989

Sometimes this interconnection uses pins, where a pin

passes through the substrate and the ﬂex cable to provided

the proper interconnection. At other times, the ﬂex cable

may be surface soldered directly to land patterns on the

hybrid circuit. Proper mechanical support, using tie-down

bars, or adhesives, shall be used to prevent stresses on the

solder joints.

5.0 Hybrid Circuit Design Requirements There are

design and documentation feature requirements that apply

to the basic layout, the artwork master, the hybrid circuit

itself, and the end-item hybrid circuit assembly. All must

be taken into consideration during the design. Therefore, it

is important to understand the relationships they have with

one another as shown in Fig. 5–1.

5.1 Design/Fabrication Sequence

5.1.1 Schematic/Logic Diagram

The initial schematic/

logic diagram designates the electrical functions and inter-

connectivity to be provided by the hybrid circuit and its

assembly. The schematic should deﬁne, when applicable,

critical circuit layout areas, shielding requirements,

grounding and power distribution requirements, the alloca-

tion of test points, and any preassigned input/out connector

locations. Schematic information may be generalized as

hard copy or computer data (manually or automated).

5.1.2 Parts List The initial Parts List should contain the

following:

A complete description of the part, quantities, manufactur-

er’s name, reference designators, and, if required, special

ordering instructions. Sometimes it is desirable to also

include the cost of the items to be used for cost analysis

purposes. The method of how the information is to be for-

matted and what must be included depends upon the stan-

dards established by each user. It is advisable to group

like-items, e.g., resistors, capacitors, integrated circuits,

etc., in some sort of ascending or numerical order. This is

of particular value to someone who must order the materi-

als.

The parts list must also have some sort of drawing number,

depending upon the design facilities system. And, in most

cases, the name of board for which it was prepared.

Included also should be the names of the persons prepar-

ing, checking, and approving this document.

Some means of identifying the revision level must also be

provided.

5.1.2.1 Non-standard Part Information When non- stan-

dard parts are used in the design, the detailed mechanical/

physical description, shall be provided as a minimum. This

information should be referenced to the schematic, so that

the appropriate layout conﬁguration can be determined.

When non-standard parts are used, usually a speciﬁcation

control drawing is required, to ensure that future parts

match the layout concepts.

5.1.3 End-product Requirements The end-product

requirements, as deﬁned in IPC-HM-860, should be known

during the design phase. In addition, the maintenance mis-

sion of the equipment is important information to insure

the correct design approach of component placement and

conductor routing.

5.1.4 Testing Requirements Normally, prior to starting

a design, a testability review meeting should be held. Test-

ability concerns, such as circuit visibility, circuit operation,

and special test requirements and speciﬁcation are dis-

cussed as a part of the test strategy. Any artwork or con-

ﬁguration concepts necessary to test the board, shall be

incorporated into the ﬁnal board layout.

During the design testability review meeting, tooling con-

cepts are established, and determinations are made as to the

most effective tool-cost versus board layout concept condi-

tions.

IPC-859-4-15

Figure 4–15 Metal electrical face (MELF) chip resistor

IPC-859-4-16

Figure 4–16 Dip socket

December 1989 IPC-D-859

During the layout process, any circuit board changes that

impact the test program, or the test tooling, shall immedi-

ately be reported to the proper individuals for determina-

tion as to the best compromise. The testing concept should

develop approaches that can check the board for problems,

and also detect fault locations wherever possible.

Figure 5–2 provides a Testability Design Check-list to be

used in evaluating the testability of the design.

5.1.5 Layout Concepts The ﬁnal layout is used for pre-

paring artwork and for fabrication and assembly of proof-

of-design and prototype hybrids. It depicts the hybrid

microcircuit as it will actually appear after assembly with

all components located in their ﬁnal positions, wire bonds

routed to the proper lands, and resistors of the proper size.

5.1.5.1 Feasibility Density Evaluation After approved

documents for the items described in 5.1.1 through 5.1.4

are provided, and before the actual drawing of the layout is

begun, a feasibility density evaluation should be made.

This should be based on the maximum size of all parts

required by the Parts List, and the space they and their

lands will require on the total circuit, exclusive of intercon-

nection conductor routing. The total circuit geometry

required for this mounting and termination of the compo-

nents should then be compared to the total usable area for

this purpose. The more reasonable the maximum values

are, the greater will be the chances for the completion of a

successful design.

5.1.5.2 Grid Systems The grid system used shall match

the requirements of the master drawing, see paragraph

3.3.3.

When component locations or other pattern features do not

end on grid, their locations are critical, and their center-

lines must be drawn or accurately deﬁned on the layout.

5.1.5.3 Viewing The layout should always be drawn as

viewed from the component side of the board. For artwork

generation purposes, paragraph 5.5, the viewing require-

ments shall be identical to the layout. (See IPC-D-310 and

Figure 3–1).

The deﬁnition of layers of the circuit shall be as viewed in

3.3.2, with distinguishing characteristics used to differenti-

ate between conductors on different layers of the circuit.

5.1.5.4 Accuracy The drawing scale used for the layout

should be sufficiently high (usually 20:1 or 40:1) to mini-

mize inaccuracies when it is being interpreted during the

artwork generation process.

5.1.5.5 Layout Notes The layout should be completed

with the addition of appropriate notations, marking require-

ments, and revisions/status level deﬁnition. It is necessary

IPC-950-4-17

Figure 4–17 Surface mount chip carrier socket

IPC-D-859 December 1989