OKI Develops Automatic Soldering Technology based on Static Pressure Bath to Enable Lead-free Soldering for Large, High-density Products

OKI expects to expand its EMS business through higher quality and shorter turnaround time

OKI Electric Industry (TSE: 6703) announced it has succeeded in developing “static pressure soldering technology” for lead-free soldering of large, high-density products. Using this technology, OKI and Nihon Dennetsu jointly developed a soldering machine that enables high-quality lead-free (Sn-3.0Ag-0.5Cu) soldering for products up to 490 x 510mm in size and 6mm in thickness.

“We believe this new ‘static pressure soldering technology’ will improve the soldering quality and production service for large, high density products at our EMS business in the Systems Network Plant in Japan’s Honjo district (Saitama Prefecture),” said Koh Shimizu, General Manager of EMS Business Manufacturing Service at OKI’s System Network Plant. “As this technology becomes our competitive strength in the EMS business, we will be applying this to manufacture information and telecom equipment, measuring equipment and medical equipment.”

In the industrial electronics field, which is a core area of the electronics industry, machines are becoming faster and more highly integrated. In accordance, printed wire boards(*1) (PWBs) are becoming larger and multilayered, while the shapes of devices are more diverse. On the other hand, from an environmental protection standpoint, there is a growing trend to use lead-free solders, making it more difficult to assemble machines.

For example, on a PWB that is 460 x 500mm in area and 4mm thick, there are cases where a mix of over 10,000 surface-mounted components(*2) and insertion components(*3) must be soldered to it using lead-free material. To make this more of a challenge, installing an insertion component requires one to first perform reflow soldering(*4) of the surface-mounted components on both sides of the PWB, then insert the component terminal in the PWB’s through-hole(*5), and then perform soldering. However, when using conventional soldering irons or flow soldering machines(*6), under filling of the through-hole can occur due to lack of heat or non-stable solder filling. Moreover, when applying a high degree of heat on a certain part using a solder iron to avoid under filling, it may cut the internal layer pattern of the PWB. Even with a flow soldering machine, if the soldering contact time is too long, the copper may melt, causing damage to the PWB pad patterns(*7) on the PWB. These are the issues that must be solved when offering a soldering method for large, high-density products.

OKI’s newly developed “static pressure soldering technology” will ensure a decent soldering filling without damaging the PWB and will enable partial soldering for insertion components on large high-density products. In addition, with the new soldering machine based on this technology, OKI enables manufacturing of large, high density products of higher quality and with shorter turn around times.
About “static pressure soldering technology”

Conventionally, soldering was performed by creating waves on a molten solder bath which would then wet the PWB surface with solder. However, there were cases where defects occur when it was difficult to fill the through-holes with solder, as distortion in the waves occurred depending on the condition of the PWB (i.e. design and the shape of mounted components). This difficulty also became pronounced as PWBs became thicker. OKI’s “static pressure soldering technology” successfully solders though-holes by controlling the solder liquid level to solve these flow soldering issues and by controlling the depth of dip(*8) of PWB.

About the new soldering machine using “Static pressure soldering technology”

The soldering machine jointly developed by OKI and Nihon Dennetsu consists of sections for preheat and soldering.

In the preheat section, by using a tact flow(*9) and heater controlled by PID control(*10), the machine can preheat the PBC and gradually apply heat. This avoids heat overload in any section and thus prevents cutting the inner layer pattern. By adopting “static pressure soldering technology” to the soldering section, it can control the solder flow almost completely, and prevent damage to the PWB pad patterns. Moreover, by enabling preliminary heat to be applied in the preheat mechanism and adopting accurate control of liquid level depth in the soldering mechanism, OKI succeeds in enabling steady solder injection into the through-hole and reliable soldering filling. While conventional flow soldering machines had a 50% through-hole solder filling rate on a 6mm PWB, the new machine achieves a 100% rate.

Glossary

* *1 :PWB (Printed Wire Board)

This is a board with electric circuit wiring with conductor such as copper foils on insulation base material. It functions as a circuit by installing electronic parts such as semiconductors, resistance, and capacitors, and connecting it by soldering.
* *2 :Surface-mounted components

These are electronic parts that can be installed on the surface of the printed circuit board only by soldering. The components can be mounted on the surface as the components include a small amount of soldering material for bonding or have lead pins on the terminals.
* *3 :Insertion components

These are electronic parts that are made to be inserted or soldered in the through-hole of PWBs.
* *4 :Reflow soldering

This is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used on the board to place the electronic components, after which heat is applied to melt the solder.
* *5 :Through-hole

A hole in PWBs that is coated with copper or other metal coating to electronically connect the inner and outer layer, and that is also used as soldering insertion components.
* *6 :Flow soldering machine

This is a soldering machine done by creating waves on a molten solder bath through flow method.
* *7 :Damage on pad patterns

This is a symptom when the pad pattern, the copper element in the PWB spreads, melts and erodes into the solder.
* *8 :Depth of dip

This is a depth to soak the electronic component or assembled PWB in the soldering bath.
* *9 :Tact flow

This is a method to feed not in a constant speed, but by repeating to proceeding, and stopping in the divided zone.
* *10 :PID control

This is a controller and function that includes the three actions: proportional action, integral action and derivative action.

About Oki Electric Industry Co., Ltd.

Founded in 1881, Oki Electric Industry Co., Ltd. is Japan’s first telecommunications manufacturer, with its headquarters in Tokyo, Japan. OKI provides top-quality products, technologies and solutions to its customers through its info-telecom system business and printer business. All businesses function as a collective force to create exciting new products and technologies that satisfy a spectrum of customer needs in various markets. Visit OKI’s global web site at http://www.oki.com/.

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