July, 2019


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Handling Risk Mitigation in Hand Soldering: Questions and Concerns


Continued from previous page


mined time cycle, since there is no capability to adjust, once the tip touches the joint. Therefore, in terms of process control, these are “open-loop” sys- tems.


Although designated as validation systems,


these systems typically incorporate some predeter- mined programs to manage time, with no ability on a real-time basis to incorporate critical vari- ables, which might influence the soldering process. In this respect, it is somewhat ques- tionable whether the output from from the system and green or red LEDs have any real “fail-safe” validity. To support these conclusions, the


following questions and considera- tions should be reviewed. These sys- tems state that the visual standard and operator skill do not account for the correct formation of the inter- metallic compound.


Three-Step Simulation Manual hand soldering takes


place in an open environment. Therefore, to properly set up these types of systems, it would be reason- able to assume that all variables need to be controlled, including the follow- ing: the type of solder in use, multiple layer PCBs, pad size, component pin size, operator skill and method of operation, tip geometries, tip idle temperature, and the flux in use. Do these sol- dering systems incorporate these considerations when the solder tip touches each joint? Note: Intermetallic formation begins at room


temperature. For lead-free applications, it is gen- erally accepted that the correct formation of the intermetallic compound at the solder joint is approximately 104°F (40°C) above the solder melt temperature. In a closed environment, a typical reflow oven for lead-free is set at 491°F (255°C). Soldering systems such as these use software


to execute algorithms required to run the proce- dures, for the three “detection phases.”


Step 1: Based on information from these hand sol- dering systems, the preliminary validation is done when they compare the thermal characteristics of tip geometry and the power delivered to the joint, within two seconds of applying the tip to the load. As there are different load requirements for


each pad, depending on what traces or pins are behind the joint, identification of the tip geometry


Information from these systems states that


once liquidus occurs, thermal resistivity becomes stable and power decreases. However, in certain applications, there are two potential reasons why power decreases. These occur when tips with smaller geometries are used on a multilayer PCB with small component leads. In this case, even if the pad does not drain the heat from the tip, the heater and the tip will reach equilibrium. Therefore, two possible equilibrium states exist: Power decreases due to the equilibri- um between the heater/tip and joint, or power decreases between the heater and the tip itself. The majority of applications


where small geometry tips are used are at high temperatures. As such, it is difficult for systems to differentiate between these two phenomena, lead- ing to a potentially incorrect assump- tion by these hand soldering systems’ software/hardware. For different solders, the rates of


Preliminary validation.


and load is difficult to establish and then process. Even if the EPROM can store tip data, load will still vary from PCB to PCB. Generally, three loads exist within these sol-


dering systems: large load/high power, medium load/medium power, and small load/small power. Since they use Curie heat technology, which oper- ates on a “power on demand” basis, different levels of power delivery will be required, depending on the position between the solder tip and the joint. However it is the function of the contact area that determines how much power is “drained” when the tip touches the pad and then the subsequent reduction in tip temperature.


intermetallic growth with other metals that dissolve into the molten solder will vary and need to be controlled. The growth of the intermetallic phase is a function of time and temperature, with temperature having a significant influ- ence on the growth rate.


For example, when PCBs with tin/solder


tracks and pads are transported by sea container, where internal container temperatures reach around 149°F (69°C), the intermetallic phase can grow up to 0.42 µm after four weeks of transporta- tion. This value corresponds to a storage period of 12 months at 71.6°F (22°C). Since intermetallic growth begins at Step 1, it is not clear from these soldering systems whether this phase of the inter- metallic growth is calculated.


Step 2: At this stage, these types of soldering sys- tems are set to detect that the solder is in a liq-


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