One · Profile's importance in reflow soldering

Reflow soldering is a main method to form solder joints on SMT base-panels and so is a core technology in SMT process. Defects caused by improper design of surface-mount PCBs, solder paste printing and component mounting will eventually find expression in soldered products.

I.C.T is a manufacturer of SMT machines. It mainly provides customers with SMT production lines including SMT Stencil Printers,  Pick and place machines, Reflow Oven, AOI Machine, Wave Soldering Machine and PCB Handling Machine etc. I.C.T has more than 25 researches on SMT and DIP technology,  for the world Customers provide SMT total solutions. There are successful cases of SMT technICal team in Asia, Europe, AmerICa, AfrICa, and Australia.

The purposes of all process controls during surface mounting are to realize high soldering quality. If there is no reasonable and feasible reflow soldering process, any process control before said makes no sense. The form of reflow soldering process mainly is the profile, referring to the curve of temperature change over time which is tested on SMT component. Thus, profile is an important factor to decide soldering defects. Defects caused by inappropriate profile mainly include cracks, warped components, tin sweats, bridging, Pseudo soldering, cold soldering, PCB delamination or blister, etc. Therefore, appropriate design of profile can result in higher yield and reliability and reasonable control of profile has a pivotal role in soldering process.

Two - Reflow profiles' general technical requirements and main forms

1. Profiles' general technical requirements for each stage, In general, profile can be divided into three stages: Preheating, reflow soldering and cooling.

Preheating: Preheating refers to heating which is to activate the flux and avoid any defect due to rapid heating when component is

soldered.

Preheat temperature: Temperature is set according to what solder paste is used and what conditions are recommended by manufacturers.

Generally, it is set at 80~160 "C and temperature should rise slowly (to get the best profile). For traditional profile, constant temperature zone lies between 140~160 "C .

Please note that high temperature results in much faster oxidation. In high-temperature zone, oxidation speed may increase in a linear way; if it is preheated to about 150 "C , oxidation rate may be several times of that in room temperature.

Please see attached figure for the relationship between copper plate temperature and oxidation speed). If preheat temperature is too low, flux may not be activated fully.

Preheat time: It depends on the component with highest heat capacity, PCB area, PCB thickness and performance of solder paste used.

Generally, 80~160"C preheat stage takes 60 ~120 seconds, thus effectively removing the volatile solvent in solder paste, reducing the thermal shock for component, getting flux fully activated and temperature difference smaller.

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