Pulsed-Heated Hot-Bar Reflow Soldering is actually 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 between the parts and solder. Pulse heated soldering differs from the traditional soldering process in this the reflow of solder is accomplished employing a heating element called a thermode which can be heated and cooled down for every connection. Pressure is applied in the entire cycle including heating, reflow, and cooling. This technique is most frequently employed to connect flexfoils to Printed Circuit Boards.
With hot bar soldering machine is applied throughout the entire cycle,including heating, reflow and cooling. Because pressure is appliedduring the entire cycle, the process is very suitable for parts that will jump loose during cooling down when soldered with some other techniques. Typical application examples are flexfoils, small wires, very light or small components, etc. The positioning of the parts is incredibly accurate because the pressure is used during cooling down. For components which require an incredibly precise positioning after being soldered HBR Soldering is easily the most ideal process.
And opposed to traditional soldering, pulse-heated soldering reflows solder simply by using a thermode which is heated and cooled down for each and every connection. This selective heating-up of simply a small portion of the components helps make the process very appropriate for soldering heat-sensitive parts. Typical application examples are CCD camera chips, connectors, etc.
With HBR Soldering all connections to become made simultaneously. As much as 200 leads or wires can be connected in a process cycle (typically around 15 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 power production of a quality hot-bar is quite high. A hot-bar as small as 10mm can generate as much as 4000 Watt compared to maximum 50 Watt for a conventional solder iron and 30 Watt for diode laser soldering. This lets short process times and good solder results on parts using a high-energy requirement, like MCPCB and ceramics. HBR Soldering can be a method that is reproducible, quantifiable, and traceable to quality standards like ISO / NIST. It can be safe for that operator, highly operator independent and simple to automate.
The New-Bar or thermode is mounted into a bonding head through a quick connect block. The bonding head has a accurate and stable linear guidance for your hot-bar. Movement is completed using a pneumatic cylinder or perhaps electrical motor. An inside spring system generated a correct force. Most reflow joints with this nature require fewer than 100 Newton pressure. Force ought to be calibrated and set up on the correct level to obtain the right transfer of thermal energy on the solder joint. The bonding head needs to have a precise coplanarity adjustment to create the flatness in the thermode on the product accurately. These heads are modular in construction and for that reason versatile for integration.
Once the start signal is provided, the Robotic Soldering Machine is gently lowered until it seats on the product. Your head senses this. Force is build-up before the preset force is reached. Once the right force is reached, a signal is passed for the power supply, which starts warming up the-bar.
Presently, the new-bar holds across the product with all the preset force. The hot-bar is in “room temperature”. The solder control unit, also called “SCU” or “power supply” has received the start signal to the soldering process.
The SCU sends current with the hot-bar. The new-bar is created to ensure the electrical resistance is highest at the bottom (where it touches the product). Heat is generated as a result of combination of current and electrical resistance. A little thermocouple is welded around the front of thermocouple. This thermocouple feeds back the exact hot-bar temperature for the SCU. This makes a total closed-loop regulation for that temperature-time cycle.
Normal rise time for many hot-bars is 1.5 to 2 seconds, equalling a heating rate of around 200 degrees Celsius a second. The newest generation of solder control unit is controlling the temperature all the way through the warming up phase. If the “REFLOW temperature” is nearly reached the solder control unit has to 15dexopky across the heating rate to prevent a temperature overshoot. An effective solder control unit and hot-bar combination will compensate for all differences in heat-loads that may occur during normal production circumstances.
This design has each side of the polyimide (kapton) material removed, leaving the traces free from insulation. The-bar contacts the traces directly and conducts heat towards the parts. In the event the PCB pads and hot-bar footprint are sized correctly, this design will probably be most tolerant to excess solder around the pads, as solder may flow into open areas. During the process, solder may also wet to the peak in the trace. Caution has to be exercised partly handling as the traces might be easily bent or damaged. Due to the direct hot-bar to lead contact, this design may have low hot-bar temperatures and short process times. The new-bar will pollute with flux residues, and definately will require cleaning. A kapton feeder module (view the section on equipment) will solve these objections.
This design has got the polyimide removed on one side only. Heat is conducted from your hot-bar with the solid polyimide surface on the exposed traces
underneath. The polyimide conducts heat from the insulation for the exposed traces and pads in the PCB. The polyimide thickness in the joint area has limitations to about 50 microns, enabling conduction. In the event the LED Soldering Machine should be heated past 400 – 425°C, burning of polyimide and hot-bar contamination might result. This design is less tolerant of excess solder in the PCB pads because little room exists for excess to circulate. The one-sided flex is best option for small pitches. Pitches as small as 200 micron, arranged in a couple of rows, are possible.