Pulsed-Heated Hot-Bar Reflow Soldering is really a selective soldering process where two pre-fluxed, solder coated parts are heated to some temperature sufficient to cause the solder to melt, flow, and solidify, forming a lasting electro-mechanical bond in between the parts and solder. Pulse heated soldering differs from the conventional soldering process in that the reflow of solder is accomplished employing a heating element known as a thermode that is heated and cooled off for every connection. Pressure is applied through the entire cycle including heating, reflow, and cooling. This method is mostly used to connect flexfoils to Printed Circuit Boards.
With hot bar soldering machine is used throughout the entire cycle,including heating, reflow and cooling. Because pressure is appliedduring the total cycle, the process is very suitable for parts that could jump loose during cooling down when soldered with other techniques. Typical application examples are flexfoils, small wires, very light or small components, etc. The position of the parts is extremely accurate as the pressure is applied during cooling down. For components which require a really precise positioning after being soldered HBR Soldering is regarded as the ideal process.
And in opposition to traditional soldering, pulse-heated soldering reflows solder simply by using a thermode that is heated and cooled down for each and every connection. This selective heating-up of merely a small portion of the components helps make the process very suitable for soldering heat-sensitive parts. Typical application examples are CCD camera chips, connectors, etc.
With HBR Soldering all connections being made simultaneously. Around 200 leads or wires may be connected in one process cycle (typically around just a few seconds). Making the connections simultaneously also prevents one wire jumping loose while
soldering the neighboring one. Typical application examples are multiple small coax cables. The strength output of a top quality hot-bar is extremely high. A hot-bar as small as 10mm can generate approximately 4000 Watt in comparison to maximum 50 Watt to get a conventional solder iron and 30 Watt for diode laser soldering. This enables short process times and good solder results on parts by using a high-energy requirement, like MCPCB and ceramics. HBR Soldering can be a procedure that is reproducible, quantifiable, and traceable to quality standards like ISO / NIST. It really is safe for the operator, highly operator independent and easy to automate.
The New-Bar or thermode is mounted to your bonding head by means of a quick connect block. The bonding head has an accurate and stable linear guidance to the hot-bar. Movement is carried out using a pneumatic cylinder or even an electrical motor. An internal spring system generated an accurate force. Most reflow joints on this nature require less than 100 Newton pressure. Force must be calibrated and set to the correct level to get the right transfer of thermal energy to the solder joint. The bonding head should have an accurate coplanarity adjustment setting the flatness in the thermode on the product accurately. These heads are modular in construction and therefore versatile for integration.
After the start signal is provided, the Robotic Soldering Machine is gently lowered until it seats about the product. The head senses this. Force is build-up until the preset force is reached. When the right force is reached, a transmission is passed on the power source, which starts warming up the recent-bar.
Right now, the-bar holds on the product using the preset force. The-bar are at “room temperature”. The solder control unit, also called “SCU” or “power supply” has gotten the beginning signal for that soldering process.
The SCU sends current with the hot-bar. The recent-bar is created in order that the electrical resistance is highest at the bottom (where it touches the item). Heat is generated because of the mix of current and electrical resistance. A little thermocouple is welded on the front of thermocouple. This thermocouple feeds back the exact hot-bar temperature to the SCU. This makes an entire closed-loop regulation for your temperature-time cycle.
Normal rise time for the majority of hot-bars is 1.5 to 2 seconds, equalling a heating rate of about 200 degrees Celsius a second. The newest generation of solder control unit is governing the temperature right through the warming up phase. Once the “REFLOW temperature” is almost reached the solder control unit must 15dexopky across the heating rate to prevent a temperature overshoot. An excellent solder control unit and hot-bar combination will compensate for all variations in heat-loads that can occur during normal production circumstances.
This design has each side in the polyimide (kapton) material removed, leaving the traces clear of insulation. The hot-bar contacts the traces directly and conducts heat for the parts. When the PCB pads and hot-bar footprint are sized correctly, this design will be most tolerant to excess solder in the pads, as solder may flow into open areas. Along the way, solder may also wet to the peak of your trace. Caution should be exercised to some extent handling because the traces can be easily bent or damaged. As a result of direct hot-bar to lead contact, this design can have low hot-bar temperatures and short process times. The new-bar will pollute with flux residues, and can require cleaning. A kapton feeder module (start to see the section on equipment) will solve these objections.
This design offers the polyimide removed in one side only. Heat is conducted through the hot-bar through the solid polyimide surface on the exposed traces
underneath. The polyimide conducts heat throughout the insulation on the exposed traces and pads about the PCB. The polyimide thickness inside the joint area is restricted to around 50 microns, enabling conduction. In the event the LED Soldering Machine has to be heated past 400 – 425°C, burning of polyimide and hot-bar contamination might occur. This design is less tolerant of excess solder about the PCB pads because little room are available for excess to circulate. The single-sided flex is best option for small pitches. Pitches no more than 200 micron, arranged in a couple of rows, are possible.