Metal fusion bonding – With control means responsive to sensed condition – Work-responsive
Patent
1996-08-13
1998-06-23
Heinrich, Samuel M.
Metal fusion bonding
With control means responsive to sensed condition
Work-responsive
228 59, 219388, 219405, 219 3512, B23K 3047, B23K 1008
Patent
active
057693048
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The invention relates to a Surface Mounted Device (SMD) soldering apparatus. For mounting the components on the upside wiring the so-called reflow soldering is used. The soldering spots are provided with solder paste--preferably by means of respective handling apparatuses--, and the board is provided with the components, preferably also by means of handling apparatuses. Thereafter the component-carrying circuit board (hereinafter "board") is heated, preferably by heat radiation, up to the soldering temperature. The heating is usually implemented in three temperature steps. In a first step, heating up to about 100.degree. C. in order to remove solvents in the solder paste. In a second step, the board is heated to a temperature little below the solder melting temperature in an attempt to bring the entire board to substantially uniform temperature. In a third step, the solder is molten.
Known SMD reflow soldering installations are designed as tunnel furnaces through which the boards are continuously conveyed.
The known installations have some weaknesses.
Some SMD components, in particular semiconductor circuits, are conceived such that they support the melting temperature of the solder over a short time interval. Consequently, the third temperature step should be as short as possible. On the other hand, however, melting of all solder spots must be assured. With the known installations, several trials will have to be executed for a certain type of circuit in order to adjust the parameters properly. Nevertheless, the number of rejects is high, and repairs, if at all possible, require considerable effort.
It is a matter of course that such conveyer soldering installations are conceived for mass production because the high trial and reject rate would not be economically feasible for production of individual boards or a small series of boards.
A third drawback of the known installations is their conceptual basis to heat the entire board as uniformly as possible up to the melting point of the solder. This forces the designer to distribute the components in a similarly uniform pattern on the board surface regardless of their functional interaction and with a resulting disadvantageous wiring.
SUMMARY
It is the object of the present invention to eliminate or at least to reduce at least some of the drawbacks of the prior art mentioned above.
According to a first aspect, the invention provides not to determine the soldering parameters (temperature-time-control) by trial and error but that the very melting of the solder is monitored so that immediately thereafter heating may be stopped. To do so, preferably the phenomenon is utilized that the solder paste which is stump-grey below the melting point will radically change its reflectance upon melting, this being detectable by means of, for example a video camera.
This also removes the obstacle for utilizing SMD technique with individual boards or small series of boards so that instead of a conveyer furnace an apparatus may be used for single boards. In this apparatus, the three temperature-time-processes are successively implemented. In accordance with a further aspect of the invention, however, such apparatus may be modified for larger series in that it is preceded by a tunnel conveyer furnace wherein the first two heating steps are implemented while the supplemented apparatus will implement only the last, terminating step. It will be understood that the conveying will then not be continuous but occur in steps.
The fact that the board during soldering is stationary will facilitate application of a third aspect of the present invention. According thereto, a device is provided which permits to mask select areas of a board over selected time intervals so that other areas having higher heat absorption (e.g. heat sinks) are heated over a longer time period. In this way, the designer is free from the restrictions mentioned above.
A preferred embodiment of the invention will be explained hereunder with reference to the accompanying drawings. The illustrations are
Caserza Steven F.
Fredart Sondermaschinen GmbH
Heinrich Samuel M.
LandOfFree
SMD soldering apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with SMD soldering apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and SMD soldering apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1387193