Metal fusion bonding – With means to remove – compact – or shape applied flux or filler – By fluid blast or suction
Patent
1992-04-30
1993-06-29
Heinrich, Samuel M.
Metal fusion bonding
With means to remove, compact, or shape applied flux or filler
By fluid blast or suction
228 37, 228254, 118 63, B23K 100
Patent
active
052226506
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a horizontal solder leveller.
The term "horizontal solder leveller" means a machine through which printed circuit boards and the like (hereinafter called "boards") are passed substantially horizontally for application of molten solder and levelling of the applied solder. Accordingly such a machine comprises at least means for applying molten solder and means for levelling the applied solder. A horizontal solder leveller is described in specification No: WO 87/07196, published on 3rd Dec., 1987, of my international patent application No: PCT/GB 87/00367.
Where the solder levelling means are so called "air knives", i.e. nozzles for directing air jets at a board having its solder levelled, molten solder blown from a board during levelling forms solid particles which are blown in the general direction of the solder application means. However considerable quantities of the particulate solder are liable to form unwanted deposits on various parts of the machine. These deposits are inconvenient and must be removed periodically.
It is conventional in solder levelling to apply oxidation inhibiting oil to boards being tinned, since this is known to improve the quality of the tinning. In the machine of my earlier mentioned patent application the oil was applied by passing the board through a layer of oil overlying molten solder in a solder bath.
Operation of the earlier machine left room for improvement as regards unwanted solder deposits and quality of tinning. The object of the present invention is to improve these factors-not only in my earlier machine, but generally in horizontal solder levellers. To this end, I now provide a dispersion of oil in the air flow from the air knives. The dispersion intermixes with the blown solder and causes, I believe, collision of solder particles with oil droplets which act to decelerate the solder blown from the board by the air knives and to coat the solder particles with oxidation inhibiting oil. Further, it keeps the machine generally covered in oil which deters solder particles from adhering to parts of the machine.
Accordingly a horizontal solder leveller of the present invention comprises:
means including a solder bath for applying molten solder to a board;
means for levelling solder applied to the board, including nozzles for directing solder--levelling air jets at the board; and
means for creating a dispersion of oil in an air stream from the levelling means, the oil dispersion means being provided between the solder applying means and the levelling means.
Preferably the solder leveller includes a pump for directly or indirectly pumping oil to the means for creating an oil dispersion.
The oil dispersion means may take various forms. It may comprise a pipe having oil dispersion nozzles from which a spray or curtain of oil is pumped directly into the airstream. This may be up- or down-stream of or at an outfeed roller pair between the solder applying and solder levelling means. One, other or both of the outfeed rollers is preferably castellated for passage of air through it.
It is not necessary for the oil to be pumped to the airstream. In the preferred embodiment, the lower one of the outfeed rollers is at least partially immersed in an oil bath and both of these rollers are castellated, that is to say has a series of smaller diameter portions between full diameter portions. These rollers are constantly wetted with oil from the oil bath, and the castellations or at least the gaps between them, provide passages for air from air knives in the levelling means. When the air knives are actuated--preferably intermittently--the air flow strips oil from the rollers to form the dispersion of it in air. Thus the oil is blown onto the board as it leaves the solder applying means and onto the machine generally. The solder spray particles from the air knives encounter oil droplets and lose momentum and/or encounter parts of the machine which are thus oiled and the solder does not adhere to the parts. In the preferred embodiment, the solder application me
REFERENCES:
patent: 4402448 (1983-09-01), O'Rourke
patent: 4921156 (1990-05-01), Hohnerlein
patent: 4928869 (1990-05-01), Lymn
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