Efficient line changeover: the key to lean manufacturing
! !
Figure 2. Typical screen printer changeover operations in minutes. Figure 3. Typical placement equipment changeover operations in minutes.
expensive solutions. Custom milled sup- ing quality issues due to inadequate board improvements have resulted in improved
port plates are one answer. These plates support or unacceptable changeover/setup print quality; however, support tooling still
accomplish the support needs but are not times will benefit. remains as the largest component of the
suitable for flexible manufacturing because In order to overcome the density screen printer changeover process as shown
of their cost and turnaround time. Other problems associated with current SMT as- in Figure 2.
alternatives, such as programmable pin semblies, this new generation of substrate The area of adequate substrate support
placement, have also become all but obso- support systems utilizes a concept similar is still an ongoing quest. For screen printer
lete due to lack of flexibility. The challenge to a ‘bed of nails.’ The system is comprised users and manufacturers, the requirement
is to meet these ever-increasing demands of any number of pins each independently for proper support is well known. In fact,
and still have a support technique that movable and lockable. Some models are proper support might arguably be the
is flexible and cost effective and can be pneumatically activated while others are single most important process parameter
changed over quickly. spring loaded. In either case, the units are to a successful print. Without it, solder
Solid support is needed during the positioned in the printer or placement bridging, insufficient solder or too much
placement process to address density, com- machine, the PCB is transferred in, and solder can result.
ponent size and the conversion to lead free the tooling pins are raised and contact
solders. With the increased density of un- the board and are locked into place. The Placement equipment
derside components, this alone is causing innovation is that the support pins of the The greatest changeover/setup demand for
operators to devote enormous time looking support system contact both bare board placement equipment is the time required
for open landing areas to place support. and components, irrespective of differences to change feeders, the programming and
In some cases this is becoming almost in component height and position. The the board support setup, as shown in Figure
impossible. Even when bottom-side space pins, made of a soft, compliant material, 3. Feeders and programming have been
is available, it may be difficult to locate eliminate concern for damage to the board a focus for quite some time with, many
them. Add to that the introduction of lead- or components. equipment manufacturers now offering
free solders, which lack the ‘self correcting’ What is achieved by using this type of feeder trolley systems that allow the opera-
characteristics of eutectic paste during the substrate support system is 100% support tor to ‘kit’ feeders offline. Other features,
reflow process, and accurate placement is a integrity, thus eliminating printing and such as tape splicing, component and reel
must. Without proper support during the placement defects caused by inadequate verification, offline programming and ma-
placement process, the natural ‘bouncing’ board support as well as a dramatic reduc- chine optimization, are now commonplace.
caused by the placement nozzle contact- tion in changeover/setup time. The emphasis on board support for
ing the board adversely affects placement pick and place machines, however, is
accuracy. setup and changeover challenges a relatively new one. In the past, most
Because of these issues, it has become We will explore, in general, the non- machines were supplied with rudimentary
a necessity to upgrade the support tooling maintenance-related factors that contribute support. These have become glaringly
in the majority of screen printers and to downtime of the screen printer and inadequate, causing placement machines
placement equipment. What is needed is placement equipment and, specifically, of to now share some of the same challenges
a highly flexible, easy-to-setup and highly substrate support. as screen printers. Whereas printers need
reliable tooling method. print deposition precision, pick and
Recent developments in substrate Screen printers place machines need placement accuracy.
support tooling have enabled companies Many advances have been made to improv- Improved support has now taken on an
to meet these quality requirements and ing the utilization of screen printers. increased importance to achieve and assure
realize substantial savings. A new family of Features such as automatic stencil loading, placement accuracy.
substrate support system is available that self-contained squeegee heads, vision as-
marries speed of setup, flexibility and reli- sist, programmable conveyors and offline cost of equipment utilization
ability into a single unit as shown in Figure programming have become mature features Inadequate equipment utilization or
1. Manufacturers that are either experienc- on many machines. These incremental proper utilization has many obvious and
www.globalsmt.net Global SMT & Packaging – March 2009 – 35
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