IPC-CM-770D-1996 - 第86页

January

1996

IPC-CM-770

IPC-1-00253

Figure 17-3 Typical Pin Terminals

board hole tolerance, and the number of pins to be inserted.

In general, the hole and plating tolerances for compliant

pins are wider than for non-compliant pins. Most all thick-

nesses of printed boards can be accommodated. Typical

mating interface), four sharp edges (for solderless wrap-

ping), and a uniform cross section. The finished loose pins

are usually put on a continuous secondary carrier to facili-

tate machine insertion and handling. See Figure 17-6. This

carrier strip is normally an expendable item and is not used

as part of the final product. There are other square pin sizes

manufactured with drawn wire as well as rectangular ver-

sions. These pins are designed to be used with mating con-

nectors as well as solderless wrapping.

B.

Stamped PinslPosts Square and Rectangular

These

pins, in 0.64 mm square as well as other square and rect-

angular sizes are manufactured from flat stock in a continu-

ous strip (see Figure 17-7).

The connection of stamped pins is designed to be near or

in the area of the minted board. where raw comnleted

pins are described as follows:

-Insulation

'

clearance

Conductors shall

bottom in cup

Conductor shall

be in line contact

with inner wall

of

terminal

Top route conductor

shall bottom against

bottom route conductor

L

IPC-1-00254

Figure 17-4 Typical Solder Cup Terminal

Insulation

clearance

Inspection hole

conductor visible

Insulation

IPC-I-

Figure 17-5 Typical Crimp Terminal

A.

Drawn Wire PinslPosts Square or Rectangular

A

most edges will be covered by solder or at the very ends, where

popular size in the industry is the 0.64 mm square variety. raw edges are of little consequence.

The pins are manufactured from a drawn wire. This method

of manufacture offers four smoothly finished surfaces (for

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Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

CARRIER

EXPENDABLE

STRIP

I

IPC-1-00257

I

Figure 17-6 Expendable Carrier Strip

IPC-1-00258

Figure 17-7 Stamped Pins

The cut away “carrier” is an expendable section. This type

of pin is designed to be used with matching connectors as

well as wire wrapping. By nature of manufacture, stamped

pin/posts have the disadvantage of having only two smooth

surfaces (for mating interference) and therefore sometimes

require orientation. They also have only two sharp edges

for wire wrapping.

C. Non-solder Carrying

Non-soldering type pin/posts are

designed without solder carrying capabilities and require

the addition of solder at assembly with the printed board

either through the use of solder preforms, wave soldering

methods or similar means.

These are available in stamped and drawn wire versions.

D.

Press-Fit

Press-fit solderless wrapposts are available

that provide gas-tight solderless connections to plated-

through holes through the use of their compliant retention

features (Figure

17-8).

E. Solder Carrying

Solder carrying pindposts are

designed to retain their own metered quantities of solder,

usually a tin lead alloy. The solder may be supplied in the

form of an extra thick coating on a predetermined area of

a pin. The solder “rivet” is more controllable in manufac-

ture as to quantity and position and is more stable metal-

lurgically.

This solder feature on pins, etc., lends itself to mass solder-

ing by vapor phase condensation, infrared, hot oil, and

‘4.

RETENTION AREAS

COMPLIANT COMPLIANT

TYPE TYPE

IPC-1-00259

Figure 17-8 Compliant Press-fit Pins

IPC-1-00256

Figure 17-9 Solder Carrying Pins

other such methods. Solderability should be verified in

accordance with

J-STD-002.

These products are designed to be used with mating con-

nectors as well as wire wrapping and are available in

stamped or drawn wire versions. See Figure

17-9.

17.1.3 Hook-up Wires

Interconnection wires can be

insulated or uninsulated, and solid or stranded.

Solid uninsulated wire is used for point to point connec-

tions on a printed board and in similar cases where no

flexibility is required.

Solid insulated wire is used for point to point connections

on a printed board where the wire cross printed board

traces or a potential for short circuits exists. The insulation

may be applied by the wire manufacturer (insulated wire)

or by adding insulation tubing (sleeving) to bare wire.

Solid insulated wire is also used for wire wrapping, where

the rigidity of the solid wire is required for consistent con-

nections.

Stranded uninsulated wire, by itself, is not a useful con-

figuration, since the wire strands tend to come unwrapped.

Stranded insulated wire is the type most often used for

interconnecting assemblies, and where flexibility is

required.

Wires are selected based on a large number of consider-

ations, approximately in the following order:

Flexibility required? (Select solid or stranded.)

Insulation required? (Select bare or insulated.)

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January

1996 IPC-CM-770

Current carrying capacity? (Select wire size. Table 17-1 switching circuits. In addition, because transistorized and

lists the current carrying capacity of small wires.)

integrated equipment requires relatively high currents with

Ease of handling? (Select wire size. Table 17-2 lists the

low voltages, it is essential that DC power distribution lines

breaking strength of typical small wires.)

have a low inductance and resistance with a high capaci-

tance.

17.1.4 Bus Bars

High-speed, solid-state circuits demand

distribution circuits be designed and placed with reference

area

Of

a

conductor.

to minimum noise pickup-a common source of pickup is

greater control of electrical noise. It is important that power Resistance can be reduced by increasing the cross sectional

Table 17-1 Current Carrying Capacity

of

Small Wires’

Rating for PVC

&

Similar

Low

Fusing Current Bare Wire, Rating for TFE

&

Similar High

Conductor Size AWG

Amperes

Temp Insulation. Amperes Temp. Insulation. Amperes

30

20.5 7 4 26

14.4 6 3 28

10.2 4 2

I

24

I

6

I

10

I

29.2

I

22

I

8

I

13

I

41.2

I

20

I

10

I

17

I

58.4

I

18 82.9 24 15

1.

Ratings are based on a single conductor at 30°C ambient temperature in still air. Other factors which affect the current carrying capacity of a conductor are

the length of the wire, the proximity to other wires, the cooling available, and the thickness of the insulation. Because of these variables, the data in this table

should be considered as an approximation only.

Table 17-2 Breaking Strength

of

Small Wires

Conductor Size

1.

Calculated in accordance with ASTM B-25, using an Ultimate Tensile

Strength value of 42,000 psi for annealed copper.

To obtain minimum, effective inductance, conductors must

be placed close together. In this manner, the magnetic

fields around each conductor, when

180

out of phase would

tend to cancel and reduce a possible source of noise.

Twisted pairs of wire have been used to achieve this effect-

however a twisted pair of wires has more inductance than

a laminated bus bar.

Since each flat conductor in a laminated bus bar can be

surrounded with ground shields to further reduce stray

electrical fields, the laminated bus is even more desirable

for power distribution. Moreover, the laminated bus bar

design permits maximum allowable distributed capacitance

between adjacent conductors, thereby reducing and sup-

pressing undesirable voltages, pulses, and noise.

The laminated bus bar is essentially a composite of flat

conductors isolated from each other with a dielectric mate-

rial and laminated into a rigid multiconductor unit. Due to

its physical structure, the laminated bus maintains very

definite electrical characteristics. When used as an integral

part of an electronic system it is a very stable circuit ele-

ment.

The number of conductors or levels, types and number of

terminals, size and finish of the conductor and the dielec-

tric strength required, depends upon the application.

Bus bars can be mounted vertically as illustrated in Figure

17-10, horizontally as in Figure 17-11, and are often

mounted under the DIP components as illustrated in Figure

17-12.

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IPC-1-00262

Figure 17-10 Vertically Mounted Bus Bars

17.1.5 Test Points

Test points are used for safe, reliable,

temporary access to a part of the printed wiring assembly

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