APPENDIX E: GUIDELINES FOR REFLOW SOLDERING
UNIFLOW
®
4 PULSED HEAT CONTROL
990-908 E-9
9
Flux
Flux has two important features. It conducts the heat to the solder and it promotes the wetting of the
surfaces by cleaning and removal of surface oxides. For easy to solder parts, the pulse heated soldering
process requires only a minimum of non-activated flux. No clean fluxes are commonly used. The use
of a low solids content flux is recommended. The lower solids content the less pollution of the
thermode. Any solvents present should be allowed to dry prior to commencing the soldering process.
Safety
In comparison to conventional soldering the pulse heat thermode soldering process is very safe, as the
heating element is only hot when it is pressed to the parts. In addition, only a very small amount of flux
is needed and therefore there are much less fumes generated. Operators should still be prevented from
touching the thermode during the cycle and should also be protected from entrapment hazards.
Soldering Method -- Process Steps
1. The base substrate is located in a fixture and flux applied to the pads.
2. The flex is positioned in the parts fixture ensuring alignment of both sets of pads.
3. A process start signal is given to the soldering control (footswitch input).
4. The soldering control then actuates the bonding head and thermode module to the parts.
5. At a pre set pressure the heating process is initiated.
The Heating Process
Base
Base provides an additional heating stage which is useful for heat sensitive parts. It also provides a
consistent temperature starting point for the reflow process.
Rise1
Rise time to preheat temperature is programmable and allows precise heating rate control. This again is
particularly useful where delicate substrates can be easily damaged by too fast a heating rate. Normal
rise time for most thermodes is 1.0 – 2 seconds.
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