Solder paste is an important interconnect material in electronics manufacturing, and solder paste has many properties that will affect its performance. For example, a good solder paste needs to have good solder removal and resistance to cold and heat collapse, and it also needs to have enough adhesion to stick the components to the circuit board. During reflow, the flux has the ability to remove oxides from components and circuit boards, and as the temperature increases, the components in the flux also have the ability to protect the solder powder or solder joints from oxidation. There is one solder paste-related property that has a big impact on production efficiency – Response-Pause (RTP). In daily production, it is often encountered that the production line has to be temporarily suspended, for example, when the placement machine changes accessories, if the pause time is long, some solder paste will dry and harden. At this time, the first circuit board after the resumption of production needs to be scrapped or cleaned and reprinted, and the solder paste on the stencil needs to be scraped off and re-stirred, which takes at least 10 minutes. If you experience several such pauses a day, the cumulative loss of yield over time is staggering. A good solder paste should be able to maintain its performance before it was paused, (pausing on the stencil for more than an hour without affecting the printing performance means that the paste has good pause-response performance.) And as mentioned above, when the SMT line needs to be suspended for component replacement or maintenance, those "hardened" solder pastes are paused and have a poor response. Figure 1 illustrates the relationship between the amount of tin under the three types of solder paste and the pause time, in the experiment, the solder paste is placed directly from the can to the stencil without stirring, note that the initial tin amount of solder paste 3 is only 5300mils3, and it reaches 9100mils3 after three printings; After an hour's pause, the amount of solder paste plummeted to 7500mils3. In contrast, solder paste 2 has a better amount of tin under it, and solder paste 1 is the best. 
Figure 1Response of the three solder pastes - pause the measurement.
If you have a production line that uses solder paste 3, you will have to scrap the first board after a pause. You may say that the first board after the pause is fine with a dummy board, and you can use it again next time when you wipe it off. It still takes a few minutes, and wasting a few minutes may not sound like a big deal, but from what we evaluated with our engineers, the problem still results in a 7% drop in productivity. In other words, if the production line can produce 10,000 boards in a certain period of time with a solder paste with a good pause response, then it can only produce 9,300 boards with a solder paste with a poor pause response, such as solder paste 3. The 7% loss of productivity is due to the loss of time due to reprinting after pause, SMT technology has been around for more than 40 years, and you might think that all solder pastes have good RTP. But sadly, this is not the case. Therefore, when evaluating solder paste, a good RTP is one of the primary indicators. Indium Corporation's star product
indium8.9hf
indium8.9HF Series Solder Paste - Halogen-free no-clean solder paste that has been proven and widely used in many industries such as aerospace, communications, semiconductor packaging, and automotive electronics. It enables low voiding, enhanced electrical reliability, and print stability for high-reliability electronics. Even at high temperatures and long reflows, it can still achieve high-performance welding and has good oxidation resistance.
indium8.9HF Characteristics:
1.Improves electrical reliability by enhancing surface insulation resistance (SIR) to suppress leakage current and dendrite growth.
2.Ensure low voiding rates for bottom terminal elements (e.g. QFN, DPAK, LGA).
3.Provides stability for solder paste printing:
Excellent pause-response performance, even after 60 hours of stencil resting, stable printability is maintained.
Storage at room temperature for one month will not affect printing and reflow performance.
Long shelf life, low temperature storage up to 12 months.
4.Provides excellent pin-on solder and through-hole solderability.
5.Inhibits flux diffusion and reduces flux contamination.
6.Suitable for leaded and lead-free alloys.
ronald lasky
Ronald Lasky, Senior Technical Specialist, Indium Corporation.
He has more than 30 years of experience in electronic and optoelectronic packaging at IBM, Universal Instruments and Cookson Electronics. He is the co-founder of the Engineering Certification Exam and has been involved in the development of several global industry standards for electronics assembly.
Indium Corporation is a leading global refiner, refiner, manufacturer, and leader of materials serving the global electronics, semiconductor, thin film, and thermal management markets. Its products include soldering consumables such as solder products and fluxes, brazing, thermal interface materials, sputtering targets, metals and inorganic compounds such as indium, gallium, germanium, tin, and nanofoil. Founded in 1934, Indium Corporation has technical support facilities and facilities in China, India, Germany, Malaysia, Singapore, South Korea, the United Kingdom, and the United States.