Can every operator handle your BGA rework equally well? In all but just a few situations, the answer is no. Why is this so?
Many factors come into play,
including experience, manual dexterity, and sometimes just plain talent. It's
critical to have your most experienced operators handle your most
demanding BGA rework.
there is delicacy involved in making such assignments, to make sure that all
operators understand the reasons and know that they are being treated fairly,
but that level of personnel management is not the focus of this article; here
we're dealing with the realities and challenges of BGA rework.
BGA rework arrived on the scene many years ago, a multitude of issues have
arisen. Choosing the right operator to handle your BGA rework is one of the
most critical steps when beginning the rework cycle.
It's also the most
misunderstood. In our experience, we find that BGA operators are a breed apart
from other technicians. It may not sound fair, but it's true.
rework presents new challenges for managers, planners, engineers and rework
technicians. Gone are the days when someone with a simple de-soldering tool and a
magnifier light could perform all the rework and inspection needed.
those rework personnel had to be skilled, but it was easy enough to train them
on a select set of skills, and equally easy to inspect their work.
BGA components, the rework model has changed forever. Instead of a simple
rework station, you might require an $80,000 BGA rework machine.
Instead of a
simple microscope or magnifier light for inspection, you may need a $150,000
Instead of an upper level assembler, you need a skilled operator,
one with computer skills, an understanding of solder paste, good dexterity, an
understanding of x-ray equipment, and the knowledge to interpret x-ray images.
operator is, in some ways, like a doctor. Operators that must perform BGA
rework need a broad range of skills, part operator, part technician, part
When choosing a BGA rework operator, you must begin by knowing what
these people do in detail in order to make the right choice.
basic machine operator is the person who hopefully operates under and follows
an engineer's guidance. The engineer may develop profiles, and set up tooling
and procedures, and the machine operator follows them.
the ideal situation and it sounds simple enough, but it's usually more
complicated than you may think. There are a multitude of small details that can
swamp the BGA rework process. For example, today's topflight BGA rework
machines are run by computers. These computers may look like a familiar desk
top unit, but the software is customized and often a little cranky. Many of
today's machine operators, particularly in electronics manufacturing, are just
not that computer savvy.
your engineer enjoys holding hands, the machine operator must have a firm grasp
of the computer system and its custom software. The machine operator must also
be mechanically inclined, able to adjust machine settings, and select and place
the proper tooling and nozzles. The machine operator must be skilled at proper
placement of circuit boards into rework system fixtures.
of the most critical aspects of proper BGA rework is circuit board stability
during the reflow process. Typically, the site will see reflow temperature for
30 to 90 seconds. Due to the nature of most circuit boards, the whole board
must be significantly heated to prevent bowing in the rework area. As the board
is heated it will often approach the glass transition temperature and begin to
move. Being able to fixture and support the board is a critical skill.
circuit boards have components placed under a BGA component rework site and
around the edges of circuit board. Some components may be so large that they
prevent the circuit board from sitting at the proper height for optical
alignment. Particularly vexing are the adjacent components that get in the way
of the alignment system, therein blocking the ability to properly align the BGA
component for rework. Some boards are longer than the fixturing apparatus that
the rework machine is supplied with, and may have a heavy component, such as a
transformer, hanging over the edge. As the board becomes heated and flexible,
the transformer may cause bending of the circuit board.
operator must know how to properly support the circuit board in all cases. You
may have the luxury of a second operator who will prepare the circuit board for
the machine operator, but when that is not the case, the machine operator must
have this skill.
the BGA component is removed from a circuit board, the component location must
be cleaned and prepared for placement and attachment of the new component. Your
machine operator must be knowledgeable and skillful enough to properly inspect
the site after the initial component removal.
this point and during the next step, the operator is determining if there is
any damage to the BGA pads or to the sensitive solder mask. The solder mask
prevents bridges and maintains the proper solder volume during placement.
Evaluating mask condition requires experience.
someone will have to remove the excess solder from the location. After that is
completed, hopefully without doing any damage to the sensitive solder mask, the
BGA pads have to be prepared to receive the new BGA component. Some people
swear that solder paste must be used. Others believe that bumping, or
filling the pads with solder by hand soldering, is the only way to go, and
still others believe bumping is not necessary, and simple tinning of the pads
is all that is required. Whatever your methods of choice, you'll require
someone who can perform the task properly.
the component replacement phase, the component must be precisely aligned with
the circuit board pads using a microscope-enhanced optical feature. This step
requires confidence, nerve, and good hand/eye coordination. Often, these
optical alignment systems are precisely calibrated, assuming that the component
location will be at a set height. Unfortunately, due to fixturing issues, the
board is frequently not at that height. The operator will need to make the
operator can get this far and stay on track, he or she is doing very well. You
would think that the next step, placing the component on the prepared site
would be a given. Unfortunately, more errors are encountered at this step than
at any other.
problems are due to improper fixturing, nozzle selection, poor site
preparation, poorly timed vacuum release or aggressive placement. Any one of
these issues might cause the part to slide off its precise location. Proper
placement depends on this step. A component being placed needs to be brought
into the ready position prior to reflow. That ready position is either a few
thousandths of an inch above the location, or barely touching the location.
the machine operator must also be skilled at optical and X-ray inspection.
Since BGA solder joints are under the component, the ability to view the joints
is severely limited. X-ray images are essential. Machine operators unfamiliar
with the nuances of X-ray imaging can easily be fooled by what they see.
the proper operator for this complex and demanding task may be the most
important aspect of setting the stage for successful BGA rework. For BGA
rework, it's the operator, more than the equipment, that's key. Assigning the
right operator to the right job may take some diplomacy, but in the end you
have little choice in the matter when product quality hangs in the balance.
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