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The business day of Advanet
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Advanet. Lead-free Project
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 5,000,000 tons of lead is used throughout the world per year. Of this, 270,000 tons is used in Japan, with 9,000 tons being used for soldering. As is common knowledge, moves are being made to regulate lead on a worldwide basis in terms of protecting the environment, and there is an urgent need to make soldering without using lead -in other words, "lead-free solder"-common practice. |
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Here at Advanet, we set up a lead-free project in 2003, and we have been busy preparing to ship lead-free products from 2005, one year before the European RoHS directive takes effect in July 2006.
Preparations are proceeding smoothly, and we are planning to ship lead-free compatible products from the first quarter in 2005. For a time, we expect to have difficulty acquiring lead-free compatible components, so we will use a combination of lead-free and non-lead free components. In the future, we intend to achieve a lead-free rate of 100%. |
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Types of lead-free solder currently commercially available for industrial equipment fall into the following categories.
High temperature solder
This is a high-temperature tin-silver alloy solder with a high melting point. Because it offers superior strength, it can be used in industrial equipment that requires particularly high reliability as well as electronic components and boards that use flow (insertion mounting) processes.
Medium temperature solder
We use a solder that is a tin-silver alloy with a small amount of bismuth and indium added. Because adding bismuth lowers the melting point and makes the solder easier to use, it can be used in electronic components and boards that use reflow (surface mounting) processes for general home appliances and so forth. |
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High Temperature Solder |
Medium Temperature Solder |
| Reflow |
Sn-3Ag-0.5Cu |
Sn-3Ag-8In-0.5Bi |
| Flow |
Sn-3Ag-0.5Cu Sn-0.7Cu |
None (due to high incidence of lift-off) |
| Characteristics |
Reliability is equivalent to or higher than that of Sn-Pb eutecticSoldering temperature is higher than that for Sn-Pb |
Solderability is better than that of high temperature solder |
| Points to note |
Heat resistance of boards and components |
Interface strength in Sn-Pb metallization |
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Advanet manufactures and sells boards for industrial equipment requiring high reliability. The most suitable soldering material for this is high temperature solder.
Here at Advanet, we use Sn-3Ag-0.5Cu (JEITA standard) for reflow and flow soldering. |
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Because high temperature solder has a high melting point, there are times when the temperature of a conventional reflow furnace will exceed the heat resistance of components and boards. To resolve this problem, it is necessary to use a forced circulation reflow furnace to eliminate variations in temperature inside the furnace. For mixed mounting that combines reflow and flow soldering, reflow soldered components must not be damaged by heat when they are flow soldered.
Advanet has introduced facilities that satisfy the above conditions, and we are working on new developments in certain equipment in conjunction with equipment manufacturers. |
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| In the past, we used FR-4 for printed board substrate. Then a halogen-free material that has a lower z-axis thermal expansion than FR-4 and is ideal for lead-free processes appeared on the market. Halogen is designated as a substance whose release into the environment is to be reduced, so we use halogen-free material in our lead-free compatible products in conjunction with our green procurement program. |
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| In order to guarantee a product life of 10 years or more, we carry out the following reliability tests. |
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| Test |
Conditions |
Evaluation Method |
| Temperature cycle test |
-55 to 125°C(30 min/30 min) |
Default, 200, 500, 1000 cyclesSEM cross-section view |
| Peel strength test |
-55 to 125°C(30 min/30 min) |
Default, 200, 500, 1000 cycles45°Cpeel (JISZ3198-6) |
| Shear test |
-55 to 125°C(30 min/30 min) |
Default, 200, 500, 1000 cyclesShear (JISZ3198-7) |
| Creep test |
High temperature storage at 85°C |
Creep after 1000 hours |
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With the shift to lead-free manufacturing processes, a new problem may arise.
The phenomenon involves the development of needle-shaped crystals in the surface of the tin plating that can, in the worst-case scenario, cause shorts.This is the so-called “whiskers” problem.
Whiskers did not occur in the past when tin-lead plating was used, but with the changeover to lead-free manufacturing processes using pure tin, the formation of whiskers became a possibility.
Whiskers are hair-like crystalline growths that occur on surfaces which have been plated with tin, and given this shape, they are commonly called “whiskers.” They have a diameter of about 2 microns and have been observed to grow to lengths of up to 2~3 mm.
What causes whiskers? First, there are physical factors: 2 to 3 years or more after a part is tin plated, metal atoms are extruded due to the residual stresses in the electroplated part, thus causing a whisker to be extruded and to develop. Another possible cause may be chemical, wherein fine metal grains, moisture, and the like are adsorbed by dirt and dust on the part (the plated surface), promoting surface corrosion.
Malfunctions caused by whiskers have recently been reported, particularly in connectors for closely spaced flexible cable.It is believed that the tensile stress applied to flexible cables is causing whisker formation in these cases.Advanet is working to prevent shorting malfunctions by implementing the following whisker countermeasures:. |
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Every effort should be made to avoid the spacing of connectors less than 0.5 mm apart. There are reports of malfunctions in the past. |
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Use gold plating if the use of such connectors is unavoidable.Plating on top of a foundation of nickel is an effective countermeasure. |
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Apply a sealant to connectors when gold plating is not available.Prevent whisker formation due to plating surface corrosion. |
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