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Greetings!
This summer we have been working on a NEW SMT
assembly class to teach engineers and
technicians about SMT assembly both theory
and practice.
The following topics are covered in this
newsletter:
See you at IPC Midwest or SMTAI Florida!!!!!
Don't forget to sign up for the IPC Midwest show taking place in Chicago the week of September 28. Make sure to sign up for Session S12 entitled "Rework and Repair: If You HAVE to Fix It".
This session will focus on
repair and rework, particularly in the area of
lead free. Below are the session speakers and
their topics:
BEST's SMT electronics assembly course
provides SMT technicians, SMT operators,
engineers and other personnel new to SMT
assembly with the knowledge and
understanding of the steps involved in the
manufacturing of modern electronic
assemblies. This course is meant for those
involved in electronics manufacturing who
desire a thorough understanding of the
assembly of surface mounted electronic
assemblies.
Practical assembly techniques, hands-on
demonstrations, local area plant tours and
explanations by a variety of experts in the
field as well as classroom lectures are used
to emphasize the teaching points. The student
will be exposed to 50% lab/plant tour
information with the balance being classroom
lectures.
Upon completion of the course, students
receive a BEST certificate of completion for
the completing the following topics:
Call Katy Radcliff at (847) 797-9250 for further details.
Underfills protect the active surface of the die of flip chips, BGA ad CSP package types while improving their reliability by distributing stress away from the solder interconnects. This increases the performance of products in meeting drop, shock and bend criteria. Newer underfills are specifically designed to minimize the need to scrap entire boards with high cost devices bonded on them because testing has determined that a device is defective. However, the ability of these devices to be reworked once they have been underfilled, is challenging and time-consuming. The goal of a typical underfill rework project is to remove the underfilled device replacing it with a good die. The removal of this material can be accomplished either with mechanical grinding or through high temperature vacuum extraction or hand tools depending on the modulus of elasticity of the underfill. The rework process begins with the even heating of the substrate to a temperature above the softening point of the underfill. The package is mechanically gripped or pried with enough torque to break the fillet's adhesions to the board. The chip undergoing rework is then heated above the solder reflow temperature to melt the solder connections and break down the underfill. The device is then removed from the PCB. Residual solder and underfill are cleaned off the substrate. Cleanup after chip removal removes any underfill residue and excess solder on the substrate. This part of the process must be done with extreme care in order to not damage the pads and adjacent components on the substrate. The site is then cleaned prior to inspection. Once cleanup of the substrate is complete, a new chip can be aligned, reflowed, and underfilled. Call us today to discuss your rework project at (847) 7979-9250 and ask for Laura Ripoli.
For years humanity has dreamed of a clean, inexhaustible energy source. This dream has lead many people to do what, in retrospect, seems obvious, and look upward toward nature's "fusion reactor", the sun. However, while sunlight is clean and inexhaustible, it is also dilute and intermittent. This led Peter Glaser of the Arthur D. Little Company to suggest in 1968 that solar collectors be placed in geostationary orbit. Such collectors are known as solar power satellites (SPS). The solar energy collected by an SPS would be converted into electricity, then into microwaves. The microwaves would be beamed to the Earth's surface, where they would be received and converted back into electricity by a large array of devices known as a rectifying antenna, or rectenna. (Rectification is the process by which alternating electrical current, such as that induced by a microwave beam, is converted to direct current. This direct current can then be converted to the "slower" 50 or 60 cycle alternating current that is used by homes, offices, and factories.) At geostationary orbit (36,000 kilometers or 22,000 miles high), the SPS would have a 24-hour orbital period. It would therefore always hover over the same spot on the equator and can keep its beam fixed on a position at a higher latitude. Since the Earth's axis is tilted, an SPS orbiting over the equator outlawing above or below the Earth's shadow during its daily orbit. Sunlight would not be blocked, except for a period of about an hour each night within a few weeks of the equinoxes. It is interesting to compare the availability of sunlight in space with that on Earth. A solar panel facing the sun in near-Earth space receives about 1400 watts of sunlight per square meter (130 watts per square foot). (Of course, only a fraction of this is usable due to conversion inefficiencies.) On Earth, the day-night cycle cuts this in half. The oblique angle of the sun's rays with respect to the ground cuts this in half again for a typical spot on the Earth. Solar panels on the ground can be angled upward to circumvent this, but they must then be spread out over more ground to avoid casting shadows on each other. Clouds and atmospheric dust cut the available sunlight in half again. Thus, sunlight is about eight times more abundant in geostationary orbit than it is on the Earth. Although the microwave beam from an SPS would also be dilute, it would be converted to electricity at a greater efficiency than sunlight. However, the largest cost savings in SPS versus terrestrial solar collectors may be the elimination of the need for storage at night .
Spurred on by the oil crises of the 1970's,
the US Department of Energy and NASA jointly
studied the SPS during that decade. The
result of this study was a design for an SPS
which consisted of a 5 x 10 kilometer
rectangular solar collector and a
1-kilometer-diameter circular
transmitting antenna array. The SPS would
weigh 30,000 to 50,000 metric tons. The power
would be beamed to the Earth in the form of
microwaves at a frequency of 2.45 GHz (2450
MHz), which can pass unimpeded through clouds
and rain. This frequency has been set aside
for industrial, scientific, and medical use,
and is the same frequency used in microwave
ovens. Equipment to generate the microwaves is
therefore inexpensive and readily available.
The rectenna array would be an
ellipse 10 x 13 kilometers in
size. It could be designed to let light
through, so that crops, or even solar panels,
could be placed underneath it. The amount of
power available to consumers from one such
SPS is 5 billion watts. (A typical
conventional power plant supplies 500 million
to 1 billion watts.) The reason that the SPS must be so large has to do with the physics of power beaming. The smaller the transmitter array, the larger the angle of divergence of the transmitted beam. A highly divergent beam will spread out over a great deal of land area, and may be too weak to activate the rectenna. In order to obtain a sufficiently concentrated beam, a great deal of power must be collected and fed into a large transmitter array
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