An electronics manufacturer needs experience with the printing process, specifically the paste characteristics, to avoid costly re-work on the assemblies. Often missed during inspection, a head-in-pillow (HIP) defect appears like a head resting on a pillow with a visible separation in the solder joint at the interface of the BGA sphere and reflowed paste deposit. Head-in-pillow defects, or incomplete coalescence of ball grid array (BGA) sphere and solder paste deposit, is a failure mode that has seen increased frequency since the transition to lead-free soldering. Insufficient amounts of paste result in incomplete circuits. too much solder, or the solder melts and connects too many wires (bridging), resulting in a short circuit. There are many different types of defects possible, e.g. The paste is applied to the board by jet printing, stencil printing or syringe then the components are put in place by a pick-and-place machine or by hand.Ī majority of the defects in circuit-board assembly are caused due to issues in the solder-paste printing process or due to defects in the solder paste. The sticky paste temporarily holds components in place the board is then heated, melting the paste and forming a mechanical bond as well as an electrical connection. It is also possible to solder through-hole pin in paste components by printing solder paste in and over the holes. Solder paste is used in the manufacture of printed circuit boards to connect surface mount components to pads on the board. JSTOR ( March 2017) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. Many ovens can't warm up or cool down fast enough to exceed the maximum temperature rates specified on component profiles, so the feedback loop supplied by the thermocouple may only be telling the controller to turn on and then off anyway.This article needs additional citations for verification. I agree with other posters that the simple approach of turning on the oven, waiting for the last joint to reflow, and then opening the door is effective. Manufacturers often use multiple thermocouples while they're getting the process figured out. Try to monitor the hottest and coldest points. Typically, larger components will reflow last, as well as ones closer to the front glass of the oven where it is colder. If you want more assurance that the profile is correct, you should monitor several points with thermocouples that are attached with thermally conductive paste or epoxy. Although an airborne thermocouple won't be reading the exact temperature of a particular joint, it should still allow your controller to recreate a consistent profile on a run of boards. However, for hobbyist applications, you may not need the precision. So what is the best approach to monitor the temperature?Ĭomponent size, density, ground planes and placement in the oven will all greatly affect the temperature at a particular point, so putting a thermocouple on glass won't tell you much more than putting one in air. But it would still not be perfect for every board of varying sizes. I have thought about putting a small piece of glass inside my reflow oven and attaching a thermocouple to the glass and using that to monitor the temperature because glass has a specific heat capacity very similar to that of FR4. Everyone is trying so hard to follow a specific profile as close as possible but if your feedback temperature is bogus then your controller is useless, right? The temperature of the board and the solder is going to vary based on many factors, including board size, which change the heat capacity of the board. The two profiles were very different, as expected. In my own reflow oven I soldered a thermocouple to a board and compared the board temp to a second thermocouple monitoring the air temperature. All of the DIY projects that I have read about, including the nice pre-made controller from sparkfun, utilize a simple thermocouple to monitor the air temperature. But you cannot monitor the temperature of easily unless you have an infra-red camera which is difficult to obtain on a budget. Unless I am mistaken, all of the recommended profiles that I have seen indicate the profile that the solder should undergo. I am having trouble understanding what is the best way to control the temperature. I have also seen many solder profiles as specified by the solder manufacturers, component manufacturers, and other self-proclaimed experts. I have read many website and forums about DIY reflow ovens for SMT soldering.

Solder reflow temperature