PCB TERMINAL BLOCKS PROVIDE VALUABLE ELECTRONIC

PCB TERMINAL BLOCKS

PROVIDE VALUABLE ELECTRONIC

INTERCONNECTIONS

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PCB Terminal Blocks Provide Valuable Electronic Interconnections 

Designing PCBs with terminal blocks requires

an understanding of the types of terminal

blocks available, the best way for them to

be packaged for delivery, and how to solder

them to reduce the potential for failure.

The printed circuit board (PCB) was introduced almost

90 years ago and has since seen immense changes and

improvements, bringing sophistication to the electronics

world. Printed circuit boards come in a multitude of

sizes and shapes to fit the ever-growing application base

for digital technologies. Multilayer printed circuit boards

have been assembled since the 1960s, and for most

electronic equipment, more than one PCB is used.

Early PCBs were populated with electronic components

such as transistors, diodes, resistors, and capacitors,

all having their own leads. PCBs used a through-hole

arrangement where a hole was placed in the center of a

solder pad, which allowed for the component lead to be

inserted. Once the leads were in place, the components

could be soldered to the pad on the opposite side of the

board using a number of dierent methods, including

manual soldering.

As technologies advanced, digital electronic chips were

developed with a band of pins along their outside edge,

which were oen short enough that they didn’t go

through the board. By the late 1960s, chip manufacturers

were designing and manufacturing surface-mounted

components designed to be mounted directly to the PCB,

allowing for increased manufacturing automation (see

Figure 1). Although through-hole and surface-mounted

technologies can both be used to populate a PCB,

most boards incorporate primarily surface-mounted

components. At the moment, the exception to this rule

would be larger components such as transformers and

heat-sink power electronics.

PCBs are made using substrates and laminates. The

substrate is the base material for the board, typically

some type of fiberglass or fabric that has been

reinforced with resin, creating a sti surface to house

the components so they’ll be able to withstand some

measure of shock and vibration without breaking. The

laminate is a copper clad material that is fused to the

substrate using heat and pressure, and then the copper

is etched away to form the conductive circuitry of the

PCB. Once finished, multiple PCBs can be joined to

create a multilayer board.

Interconnecting PCBs with the outside world requires

connector and terminal block manufacturers to provide

a wide array of products. Dierent industries need

dierent types of interconnections depending on the

specific needs of the application, and there are dierent

mounting methods to consider.

PCB Terminal Blocks

Printed circuit board terminal blocks should oer

highly dependable connections without the need for

wire lugs. For example, you might want to use tubular

screw clamps or box clamps for light duty applications

and screw-cage clamps for heavy-duty applications.

Figure 1: By the late 1960s, chip manufacturers were

designing surface-mounted components that attached directly

to the board for increased manufacturing automation.

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Although it is recommended that you use ferrules—

especially for export applications or when fine stranded

wires must be terminated—users can also simply strip

and insert the wire and then tighten the screw. Be sure

to use board-mounted terminal blocks that meet or

exceed most international standards and are accepted

worldwide.

The two primary types of PCB terminal blocks are screw

clamp and spring clamp designs. Screw terminal blocks

are simple to use; just insert the wire into the open

clamp, tighten the screw, and remove your screwdriver

for a reliable and safe connection. The benefit of

using a screw-type terminal block is that it can be

eectively manufactured for a wide variety of sizes

and configurations while oering the maximum in wire

eiciency and reliability to the user.

Be sure that the terminal block you select is able to

handle the physical stress of multiple wires mounted in

the same general location without putting undue stress

on the PCB. Terminal blocks must be sturdy and tough

and made from high-impact materials such as polyamide

PA66 and self-extinguishing plastics regardless of where

they are mounted. Note that most terminal blocks

are color-coded so that the user can easily determine

ground wires from hot wires and control wires.

Spring clamp terminal blocks take less time to wire

during installation. Through the use of a narrow

screwdriver or by hand while using a lever, users need

only to open a pre-loaded stainless steel spring. The

wire is then inserted into an opening in the spring leg.

Once the screwdriver is removed or the lever closed,

spring force presses the conductor against a copper-tin

plated clamp housing for a highly reliable connection.

The terminal blocks can be used with solid or stranded

wire for a very secure connection.

Another spring clamp terminal block design is made

specifically for single wire connections and allows the

wire to be pushed directly into the spring block without

using a screwdriver—for a tool-less connection—to

complete the operation. Push-in spring clamp terminal

blocks are growing in popularity based on their ease of

use (see Figure 2).

Figure 2: Illustrated are the three primary types of terminal block design.

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With spring clamp terminal blocks in general,

conductors can be terminated securely in mere seconds,

independently of one another and with absolute

reliability. This easy installation reduces wiring time by

over 50% while delivering a reliable, maintenance-free

connection independent of operator skill. Not only are

these terminal blocks versatile, oering a reliable gas-

tight connection, but they are vibration proof, having no

screw to loosen during operation.

These types of terminal blocks are particularly easier to

use with small wires than screw type terminal blocks.

They provide a fail proof and safe connection with no

torque requirements. Like other terminal blocks, spring

clamp devices accept wires with or without ferrules to

provide a completely maintenance free operation.

PCB terminal block design and manufacturing has come

a long way in the past few years due to the advancements

in materials and the needs of specific applications. Many

manufacturers oer a full line of components that fit the

broadest uses in the industry. For example, Altech has

expanded their PCB terminal block line to oer standard

single- and double-level fixed and pluggable terminal

blocks in metric and U.S. pin spacings and a wider array

of products within each pin spacing.

Mounting Types

PCB terminal blocks that are designed for fixed

mounting should oer users high densities with

maximum flexibility. Altech oers a line of PCB terminal

blocks with a modular construction that simplifies

ordering and reduces the need for extensive inventory.

Two- and three-pole modules can be interlocked to

create multipole assemblies or the company can

provide tailored assemblies to your specifications. The

company’s fixed mounted terminal blocks are available

with box clamps including wire protector or screw-

cage li type clamp operations that oer several wire

entry options to make installation and repair easy and

accessible. Li-type clamps are used in applications with

heavy-duty requirements while wire protector versions

are for cost sensitive applications.

The company’s pluggable terminal blocks are header

and plug combinations designed to speed and simplify

board replacement and reduce costly downtime. The

two-piece plug and header design requires no special

tools to operate. Headers are soldered into the board

and accept the plugs, which are easily removed for

fast, convenient board or device replacement when

necessary.

Single-mold designs are available for maximum strength.

Modular designs are also available, which are assembled

from two- and three-pole modules when a user needs

maximum flexibility to meet changing requirements.

Header configurations include vertical and horizontal,

single- and double-level with closed or open ends.

Pluggable PCB terminal blocks come with either screw

or spring clamp connection technology.

Figure 3: Pluggable terminal blocks come in header and

plug combinations designed to speed and simplify board

replacement.

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PCB Terminal Blocks Provide Valuable Electronic Interconnections 

When choosing screw technology connection types,

consider your application and maintenance needs.

When your application calls for the highest reliability

and frequent wire terminations, screw-cage li type

clamps are a solid choice. As the clamp is tightened, the

nickel-plated cage rises, pressing the wire firmly against

the busbar, ensuring a solid connection. On the other

hand, with box clamp wire protector designs, tightening

the screw presses the conductor directly against the

bottom of the clamp. These systems are a great choice

for cost-sensitive, lighter-duty applications.

PCB terminal blocks feature precision-formed or

machined metal parts, which are electrolytically plated.

Nickel or tin-plated brass cage clamps or tubes, stainless

steel wire protectors and springs, and tin-plated

solder pins satisfy the most demanding requirements.

Housings are precision-molded from self-extinguishing

UL-94 V0 polyamide, providing excellent strength and

temperature resistance. Each clamp style is oered in

metric and inch pin spacing.

Depending on the company’s products you work with,

most manufacturers have some sort of markings to

identify terminal inputs. Altech oers their users to order

hot stamp, inkjet, and laser imprinting for permanent

marking of large quantities or custom marked terminals.

Otherwise, standard marking is consecutive numbers,

le to right. Custom imprints are also available for

specific customer needs (see Figure 4).

Packaging Options for Automated

Assembly of PCB Terminal Blocks

Special packaging is oen available for terminal blocks

so customers can easily fit the products into their

particular production methodology. There are three

basic types we’ll consider here: tube packaging, tray

packaging, and tape and reel packaging. Early on, in

integrated circuit manufacturing, hard plastic tubes

were used to deliver components, including terminal

blocks (see Figure 5). Multiple tubes can be stacked and

transported within a facility or shipped while keeping

the components safe. These long tubes allow for gravity

feed systems where the components are easily available

for automatic placement machines.

Tape and reel packaging means that terminal blocks are

set into specially designed pockets in a long piece of

Figure 4: This photo illustrates the marking capabilities

available to the customer.

Figure 5: Tube packaging is most oen used for gravity feed

automation systems.

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PCB Terminal Blocks Provide Valuable Electronic Interconnections 

plastic tape (see Figure 6). The tape is sealed to keep the

components in place and then wound around a central

reel. This protects the terminal blocks from damage

during storage. Tape and reel packaging helps to feed

components into automated machinery, which can

operate much faster than other methods. Tape and reel

packaging also eliminates orientation errors in how the

components enter the system.

Tray packaging, like the name suggests, is when the

terminal blocks are available in trays (see Figure 7). This

form of packaging is designed to work with pick-and-

place machines. Trays are covered with a thin plastic to

isolate components from the outside environment. This

protection helps maintain component durability during

shipping and receiving. The added durability allows for

lower levels of production loss. Tube and tray packaging

of components allows for the safe storage and transport

of larger parts that do not fit comfortably in a tape and

reel operation.

Pros and Cons of Reflow and Wave

Soldering

For many manufacturers, reflow soldering is the most

common method of PCB soldering. The process first

applies solder paste made of a precise mixture of flux

and solder. Once applied, the PCB is placed into a reflow

oven where hot air is raised to a predetermined level

where the solder paste melts and forms the solder joints.

This process can be applied to specific parts of the PCB

as well. Reflow soldering preheats the PCB to eliminate

thermal shock during the soldering process, which

doesn’t require a lot of monitoring.

Wave soldering is most oen used when engineers need

to solder a large number of PCBs simultaneously. The

process begins by applying flux to the components that

need to be soldered. The flux cleans the metal prior to

soldering. Like reflow, a preheating cycle ensures that

thermal shock is avoided. A “wave” of solder then moves

across the PCB, soldering the components to the board.

A cooling cycle is used to permanently bond the solder in

place. If temperatures inside the wave soldering machine

are not correctly maintained, a number of failures can

occur. If the oven is too hot, the PCBs can develop cracks,

but if the soldering oven is not hot enough, cavities on

the PCB may result in conductivity issues and structural

weakness. Wave soldering machines do save a lot of

Figure 6: Tape and reel packaging is used to feed components

into automated machinery, providing a much faster deliver

than other methods.

Figure 7: Tray packaging is designed to work with pick-and-

place machines and allows for safe storage and transport of

larger parts.

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PCB Terminal Blocks Provide Valuable Electronic Interconnections 

time, initiate less warpage of PCBs, and are oen more

aordable, depending on your company’s needs.

Like the selection of any component, understanding

what’s available, how the product is packaged and

delivered (depending on your manufacturing process)

and how the product is installed, are all important

decisions. This is especially true for PCB terminal blocks.

The more engineers know about the whole process and

the needs of the user, the better decision they can make

on product type from the very beginning.

Figure 8: Besides automated soldering solutions, manual soldering if oen necessary when a PCB component needs to be

replaced.