To meet market demand for smaller, lighter, and thinner products, PC boards also need to change from Insertion mount to surface mount technology. To meet this need, we offer a line of surface mount relays. The following describes some cautions required for surface mount relay installation to prevent malfunction and incorrect operation.
1. What is a Surface Mount Relay?
1.From IMT to SMT
Conventional insertion mount technology (IMT) is now being replaced with surface mount technology (SMT).
Solid-state components such as resistors, ICs, and diodes can withstand high heat stresses from reflow soldering because they use no mechanical parts. In contrast, the conventional electro-mechanical relays consisting of solenoid coils, springs, and armatures are very sensitive to thermal stress from reflow soldering.
We applied the experience gained from our advanced relay technologies to produce high-performance electromagnetic relays compatible with surface mount technologies such as IRS and VPS.
Insertion Mount Technology vs. Surface Mount Technology
Insertion Mounting Technology (IMT)
Components' leads are inserted into lead holes of PC board and are soldered to copper pads on the other side of the board using flow-soldering techniques.
Surface Mount Technology (SMT)
Components are placed on copper pads precoated with paste solder and the board assembly is heated to solder the components on the pads (reflow soldering).
2.Features and Effects
• Allows high density mounting
• Components can be installed on both sides of a board
• Ceramic PC boards can be used
• Compatible with automatic placement by robots
• Drilling for lead holes is not required
• Compact system designs are possible due to high density mounting
|Overall cost reduction
• High heat resistance
• Anti-gas measures
The surface mount relay is manufactured with the following advanced technologies:
- Heat-resistance encapsulation technique
- Gas analysis
- Reliability assessment
- Precision molding technique for heat-resistant materials
3.Examples of SMT Applications
The following describes some examples of typical SMT applications:
1. Infrared Reflow Soldering (IRS)
IRS is the most popular reflow soldering technology now available for surface mounting. It uses a sheath heater or infrared lamp as its heat source. PC board assemblies are continuously soldered as they are transferred through a tunnel furnace comprised of a preheating, heating, and cooling-stages.
2. Vapor Phase Soldering (VPS)
With VPS technology, PCB assemblies are carried through a special inactive solvent, such as Fluorinert FC-70, that has been heated to a vapor state. As the saturated vapor condenses on the PC board surface, the resulting evaporation heat provides the energy for reflow soldering.
3. Belt conveyer reflow furnace
As PCB assemblies are transferred on a thin, heat-resistant belt conveyer, they are soldered by the heat from hotplates placed beneath the conveyer belt.
4. Double Wave Soldering (DWS)
Components are glued to the PC board surface. The board assembly is transferred through a molten solder fountain (with the component side facing down), and the components are soldered to the board.
5. Other technologies
Other reflow soldering technologies include those utilizing lasers, hot air, and pulse heaters.
2. Cautions for Installation
- Mounting pads on PC boards must be designed to absorb placement errors while taking account of solderability and insulation. Refer to the suggested mounting pad layout in the application data for the required relay product.
- Paste solder may be applied on the board with screen printing or dispenser techniques. For either method, the paste solder must be coated to appropriate thickness and shapes to achieve good solder wetting and adequate insulation.
- For small, lightweight components
Such as chip components, a self-alignment effect can be expected if small placement errors exist. However, this effect is not as expected for electro-mechanical components such as relays, and they require precise positioning on their soldering pads.
- If SMT relays sustain excessive mechanical stress from the placement machine's pickup head, their performance cannot be guaranteed.
- Our SMT relays are supplied in stick packaging compatible with automatic placement processes. We also offer tape packaging at customer request.
Direction A: Less than 9.8 N (less than 1,000 gf)
Direction B: Less than 9.8 N (less than 1,000 gf)
Direction C: Less than 9.8 N (less than 1,000 gf)
(ex. TQ-SMD Relay)
- Reflow soldering under inadequate soldering conditions may result in unreliable relay performance or even physical damage to the relay (even if the relay is of surface mount type with high heat resistance).
Example of Recommended Soldering Condition for Surface Mount Relays.
T1 = 150 to 180°C 302 to 356°F
T2 = 230°C 446°F or more
T3 = Less than 250°C 482°F
t1 = 60 to 120 sec.
t2 = Less than 30 sec.
- It is recommended that the soldered pad be immediately cooled to prevent thermal damage to the relay and its associated components.
- While surface mount relays are solvent washable, do not immerse the relay in cold cleaning solvent immediately after soldering.
Soldering iron tip temperature: 350°C 662°F
Soldering iron wattage: 30 to 60 watts
Soldering time: Less than 3 sec.
When a soldering technique other than above is to be used (hot air, hotplate, laser, or pulse heater technique), carefully investigate the suitability of the technique.
||The soldering temperature profile indicates the pad temperature. In some cases, the ambient temperature may be greatly increased. Check for the specific mounting condition.
- The surface mount relays are solvent washable.
- Use alcohol or an equivalent solvent for cleaning.
- Boiled cleaning is approved for surface mount relays. Ultrasonic cleaning may cause coil damage or light contact sticking.
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