CIRCUITS ASSEMBLY MAGAZINE
On The Forefront: October, 1996
Automatic Component Placement Systems
by
Phil Zarrow
At the heart of the SMT assembly process, lives the component
placement system. Also commonly called the “pick and place” machine, it is
simply a flexible machine that takes components from their “feeders” and places
them accurately onto the printed circuit board. Of course that’s where the
simplicity ends. The component placement system is usually, by far, the most
complex machine center in the assembly process. A computer controlled electromechanical “beast”, the pick and place machine is also typically the slowest
machine in the process and is thus the gating factor in through-put speed.
In the early days of surface mount technology, one of the virtues extolled
upon SMT was that it was highly automatable. With through-hole insertion, it
was expensive to automate the process. To fully automate the populating of a
typical through-hole assembly would require a sequencer and inserter for axial
leaded components (later these two machine center were combined to form one
sequencer/inserter), a radial sequencer/inserter for radial components, and a
sequencer/inserter for DIPs. These (fully automatic) machines typically cost
between $70,000 to $300,000. Consequently, it took a fairly amount of volume
to justify this cost and with labor rates much lower “off-shore” a good deal of
hand assembly was done in Asia and Mexico. By comparison a single pick and
place machine could place the surface mount equivalent of this variety of
components (axial, radial and ICs) at the cost of a single auto-insertion machine
and requiring a fraction of the factory real estate. Hence, automated assembly
was in the reach of a far wider range of assemblers. Even a “Ma and Pa” job
shop could afford a basic component placement system.
An interesting historical note is that SMT was thus touted by some as a
means of bringing electronic manufacturing back to North America and Europe
(and away form Asia) since assembly could now be done more economically.
Why it never occurred to them that the technology and its high degree of
automation wouldn’t be rapidly and very successfully implemented there as well
is a mystery. In any event, the continuation of the electronic manufacturing
services industry (EMSI) to manifest itself as the largest growing segment of the
electronics industry is largely due to the advent of SMT.
Of course, while it is true that SMT is highly automatable, in order to
assemble boards in a timely, accurate and repeatable fashion, it is highly
recommended that one does, indeed, automate. This is particularly true of the
component placement operation (as those of us who have hand-assembled SMT
boards will attest).
Regardless of the sophistication of the component placement system,
almost all of the machines on the market have “the basics” in common. The
substrate is either placed (by the operator) or automatically transported to
staging area. Components are “picked” from assigned pickup bin locations by
vacuum and usually realigned using either mechanical or optical means. The
component is then placed in its programmed location accurately. Most systems
employ vision and a host other accouterments are available to enhance accuracy
of placement, through-put speed and system flexibility.
Pick and place machines are characterized in terms of three primary
features: accuracy, speed and flexibility. Accuracy deals with the precision of
placement capability of the machine - its ability to position a component with
respect its target position on the PCB. This can be examined by measuring the
translational error (misalignment of the component centroid) and the rotational
error (angular displacement of component axes). Repeatability, the ability of the
placement system to repeatedly return to the target point, is another key
component of accuracy. Resolution, which is a measure of the finest increment
the placement machine can move, also factors in as it defines the ultimate
precision of the machine. However, it should never be used as the sole
specification for machine accuracy, as it commonly is. It is possible for one
machine with high resolution to have poorer total accuracy that a different
machine with lower resolution. The entire accuracy picture must be considered.
While the speed of the component placement system will usually be the
limiting factor in the overall line capacity, it is difficult to quantify a machines
actual speed and makes intermachine comparison perplexing. There are a
number of inter-related parameters that directly influence speed including:
 PCB board design / layout
 number of feeders
 feeder locations
 production lot size
 setup complexity
 PCB board loading program efficiency
The most commonly used data sheet specification is the equipment
placement rate. This is defined as the speed at which an average placement
cycle is completed. A placement cycle is comprised of a complete round trip
from pickup site to placement site and return. Of course, using a component
feeder in very close proximity to where it will be placed will yield the more
impressive number. Credulous suppliers will usually state the trip distance that
was used to derive their stated placement rate. While cycle rate is similar to
placement rate, it embodies operation in a dry cycle mode - without components.
Therefore, such a figure is virtually useless in terms of predicting production
throughput. The most important parameter, from a user’s point of view, is the
production throughput of a component placement system. This is defined as the
number of components placed per hour over an entire production shift:
Total # of components placed
Length of shift
For example, if 50,000 components were placed during the course of an 8 hour
shift, the production throughput would be 6,250 components/hour. Production
throughput is, hence, derived by applying some of the following derating factors:






Board load / unload time
Production mix
Machine configuration
Component mix
Available hours (in a shift)
Unscheduled downtime
For various sundry reasons, a user should never take the published throughput
specifications verbatim. The following derating factors serve as good rules of
thumb:
“PHIL FACTOR”
For Levels I through III:
55%
Equipment Manufacturer’s Specified Placement Rate x .55 =
Typical User Production Throughput
For Level IV:
90%
Equipment Manufacturer’s Specified Placement Rate x .90 =
Typical User Production Throughput
The final key area of consideration is flexibility. How adaptive is the
component system to a range of applications. Some systems are highly flexible
in that they can handle a wide range of PCB substrate sizes as well as a wide
range (and number) of component packages and respective feeders while
others, such as “chip-shooters” may be restricted to handling passives albeit at a
very high speed. Regardless of the type of system, feeder capacity is commonly
expressed in terms of the number of 8mm tape feeders that can be mounted
since almost all systems on the market can handle passives fed in this format.
Ease of setup is another contributing factor to the flexibility of a system.
Machine setup is defined as the steps necessary to change over from building
one board to another. These steps typically involve machine re-programming
and/or file downloading, feeder changeover as well as board handling width
adjustment or tooling plate changeover.
It was determined some years ago that by examining the co-relation of
flexibility and speed, a categorization of component placement systems can be
conjured. Though by far not a perfect system 1, it is useful for classification of the
automatic component placement systems on the market.
Level 1 is comprised of bench-top systems. Usually very limited in the size of
substrates they can handle as well as the number of feeders that can be
accommodated they are, nevertheless, good for prototyping, pre-production and
very short runs. Though at one time they were referred to in the field as “random
placement machines” and “pick and throw”, today’s offerings are extremely
accurate.
Level II are high flexibility machines. Some are in-line while others are quasiinline in that they can be adapted for flow-through production. They typically
handle a very wide range of component types and feed formats and many are
extremely accurate. These machines are also called flexible placement systems.
Level III are fairly flexible and are also considered flexible placement systems
because, like their slower counterparts in Level II, they handle a wide range of
component packages from passives to QFPs, SOPs and BGAs. However, they
achieve a higher throughput rate than Level II and are almost always in-line
systems.
Between Levels II and III fall the Flex-cells. These systems were discussed in
the August “On The Forefront”.
Level IV are the proverbial “chip shooters”. Limited to achieving high speed
when fed only with 8mm and 12mm tape feeders, they are extremely fast.
Always in-line, most utilize a turret-head approach.
Level V was originally classified as mass-placement machines. These highly
inflexible machines had dedicated vacuum pickups for each component. They
1
No one has yet to come up with a better system.
were limited to passives only and involved a great deal of set-up time. It is in this
area that there is equipment evolvement taking place. Systems that use multiple
heads to place six components each, arranged in-line have been introduced.
Pioneered by the Philips FCM series, though limited to passives (and hence
having low flexibility), these systems achieve very high throughput - capable of
exceeding those of their predecessors, the mass-placement machine, with
greater accuracy and lower set-up time. With costs not much greater than Level
IV systems, the configuration allows for a very small factory footprint.
There is a great deal more to component placement than can be
discussed in the confines of this column. With over 60 different manufacturers of
pick and place systems worldwide (most offering several machines within
different levels), there is a great deal of competition and equipment evolution can
be expected to continue.
Component Placement System Categorization.
Category Attributes
Typical
Throughput
< 1000 pph
Level I
Low Speed / Low Flexibility
Level II
Medium
Flexibility
Flex-cell
Low to Medium Speed / High
Flexibility
Level III
Medium to High
Medium Flexibility
Level IV
High Speed / Low Flexibility
Level V
Very High
Flexibility
Speed
Speed
/
High
Speed
/
/
Low
Suppliers
Zevatech / Juki
OK Industries
Celmacs
500 - 5000 pph
Mydata
Quad
Zevatech
Siemens
Philips
Multitroniks
Contact Systems
Celmacs
Amistar
Tescon
Sony
Citizen
100 - 4000 pph
Universal
Zevatech
Philips
3000 - 10,000 Mydata
pph
Quad
Zevatech
Siemens
Philips
Panasonic
Fuji
TDK
Universal Inst.
KME
Tescon
14,500 - 38,000 Fuji
pph
Panasonic
TDK
Sanyo
Universal Inst.
KME
40,000 - 90,000 Philips
pph
Fuji