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Quality Through People and Technology
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Amerway Inc.
3701 Beale Avenue
Altoona, PA 16601
Telephone: (800) 829-6337 Fax: (814) 944-1463
Visit our web site at: www.amerway.com
Quarterly Newsletter – October 2008
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| New Product at Amerway! |
Amerway has added ball grid arrays to their list of manufactured products available to customers. A ball grid array (BGA) is a type of surface-mount packaging used for integrated circuits.
The BGA is descended from the pin grid array (PGA), which is a package with one face covered (or partly covered) with pins in a grid pattern. These pins are used to conduct electrical signals from the integrated circuit to the printed circuit board (PCB) it is placed on. In a BGA, the pins are replaced by balls of solder stuck to the bottom of the package. The device is placed on a PCB that carries copper pads in a pattern that matches the solder balls. The assembly is then heated, either in a reflow oven or by an infrared heater, causing the solder balls to melt. Surface tension causes the molten solder to hold the package in alignment with the circuit board, at the correct separation distance, while the solder cools and solidifies.
Advantages
High Density
The BGA is a solution to the problem of producing a miniature package for an integrated circuit with many hundreds of pins. Pin grid arrays and dual-in-line surface mount (SOIC) packages were being produced with more and more pins, and with decreasing spacing between the pins, but this was causing difficulties for the soldering process. As package pins got closer together, the danger of accidentally bridging adjacent pins with solder grew. BGAs do not have this problem, because the solder is sometimes factory-applied to the package in exactly the right amount.
Heat Conduction
A further advantage of BGA packages over packages with discrete leads (i.e. packages with legs) is the lower thermal resistance between the package and the PCB. This allows heat generated by the integrated circuit inside the package to flow more easily to the PCB, preventing the chip from overheating.
Low-Inductance Leads
The shorter an electrical conductor, the lower its inductance, a property which causes unwanted distortion of signals in high-speed electronic circuits. BGAs, with their very short distance between the package and the PCB, have low inductances and therefore have far superior electrical performance to leaded devices.
BGAs find some use in security-sensitive applications, especially where it is impossible to prevent physical access to the chip. For instance, a ROM chip with a BGA configuration is considerably more difficult to access than one in a DIP or TSOP layout. Tracing circuit paths to the BGA chip is limited by the contact points being obscured by the chip itself.
Disadvantages
Noncompliant Leads
A disadvantage of BGAs, however, is that the solder balls cannot flex (non-compliant) in the way that longer leads can. As with all surface mount devices, bending, due to a difference in Coefficient of thermal expansion between PCB substrate & BGA (thermal stress), or flexing & vibration (mechanical stress) can cause the solder joints to fracture. Thermal expansion issues can be overcome by matching the mechanical and thermal characteristics of the PCB to those of the BGA. Typically, plastic BGA devices more closely match the PCB thermal characteristics than ceramic devices. Mechanical stress issues can be overcome by bonding the devices to the board through a process called "under filling", which injects an epoxy mixture under the device after it is soldered to the PCA, effectively gluing the BGA device to the PCB. There are several types of under fill materials in use with differing properties relative to reworkability and thermal transfer. Another solution to non-compliant leads is to put a
"compliant layer" in the package that allows the balls to physically move in relation to the package. This technique has become standard for packaging DRAMs in BGA packages.
Expensive Inspection
Another disadvantage of BGAs is that, once the package is soldered down, it is very difficult to look for soldering faults. X-ray machines and special microscopes have been developed to overcome this problem, but are expensive. If a BGA is found to be badly soldered, it can be removed in a , whirework stationch is a jig fitted with infrared lamp (or hot air), a thermocouple and a vacuum device for lifting the package. The BGA can be replaced with a new one, or can be refurbished or reballed. Packets of tiny ready-made solder balls are sold for this purpose.
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On August 6, 2008 the employees of Amerway attended a baseball game played by The Curve, the local farm team of the Pittsburgh Pirates.
The outing was to honor employees with 10 or more years of service and give everyone a chance to socialize with their fellow team members.
Steve Owens, scheduling manager; Bill Cover, production lead; and Ed Mullins, production received plaques for 10 years of service.
Sonny Sarosi was honored with a 15 year plaque. Everyone enjoyed the good food and thanked their team members for their valuable service.
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Trisha & Nicole
Dennis & Bunny
(background) Steve, Rachelle, Brad & Brianna
(background) Kevin
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Karen, Terry, Leah, & Tara
Brad, Karen, Den & Terry
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Solder paste (or solder cream) is a mix of microscopic solder particles and flux. It is used exclusively in the automated soldering process reflow soldering. The paste is a gray, plasticine-like material.
The solder particles are frequently an alloy of tin and lead, with possibly a tertiary metal alloyed, though environmental protection legislation is forcing a move to lead-free solder.
Solder paste is thixotropic, meaning that its viscosity changes with applied shear force (e.g. stirring). The thrixotropic index is a measure of the viscosity of the solder paste at rest, compared to 'worked' paste. Hence it may be very important to stir the solder paste before it is used.
To produce a quality solder joint, it's very important for the spheres of metal to be very regular in size and have a low level of oxide.
Solder Paste Use
Solder paste is typically used in a screen-printing process, in which paste is deposited over a stainless steel or polyester mask to create the desired pattern on a printed circuit board. The paste is dispensed pneumatically or by pin transfer (where a grid of pins are dipped in solder paste and then applied to the board).
As well as forming the solder joint itself, the paste carrier/flux must have sufficient tackiness to hold components while passing through the various processes, or perhaps moved around the factory.
Printing is followed by pre-heating and reflow (melting).
As with all fluxes used in electronics, residues left behind may be harmful to the circuit, and standards (eg J-std, JIS, IPC) exist to measure the safety of the residues left behind.
In most countries, 'no-clean' solder pastes are the most common, whereas in the US, water soluble paste (which have compulsory cleaning requirements) are common.
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Karen Horten Awarded August Employee of the Month
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| Karen Horten, purchasing agent at Amerway, was named employee of the month for August.
She joined Amerway in February of 2008 with many varied life and purchasing experiences.
Her “can do attitude” has quickly made her an integral part of the “Amerway family”.
She supports the sales team with her positive attitude and has been on a quest to find the
best products at the best prices for the entire company. For her efforts she will receive a
$75 gift certificate to the business or restaurant of her choice. Thanks Karen for all that
you do for us!
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Cory Smith Awarded September Employee of the Month
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Amerway employee Cory Smith has been described by
co-workers as a good trainer who is always willing
to chip in and help wherever needed. He steps up on his job and works hard. He
also works well with others, making his role important to the Amerway team. Congratulations
Cory!
View Past Employees of the Month
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Hilarious Signs...
On a plumber's truck:
"We repair what your husband fixed."
In a veterinarian's waiting room:
"Be back in 5 minutes. Sit! Stay!"
In a non-smoking area:
"If we see smoke, we will assume you are on fire and take appropriate action."
At an optometrist's office:
"If you don't see what you're looking for, you've come to the right place."
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Different elements serve different roles in the solder alloy:
- Silver provides mechanical strength, but has worse ductility than lead. In absence of lead, it improves resistance to fatigue from thermal cycles.
- Copper lowers the melting point, improves resistance to thermal cycle fatigue, and improves wetting properties of the molten solder. It also slows down the rate of dissolution of copper from the board and part leads in the liquid solder.
- Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn16Pb32Bi52 with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder.
- Indium lowers the melting point and improves ductility. In presence of lead it forms a ternary compound that undergoes phase change at 114 °C.
- Zinc lowers the melting point and is low-cost. However it is highly susceptible to corrosion and oxidation in air, therefore zinc-containing alloys are unsuitable for some purposes, e.g. wave soldering, and zinc-containing solder pastes have shorter shelf life than zinc-free.
- Antimony is added to increase strength without affecting wettability.
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Call Amerway's trained customer service representatives and mention code 123 to receive a
free solder pot analysis.
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