Metal fusion bonding – Process – Plural joints
Patent
1990-10-05
1994-11-29
Bradley, P. Austin
Metal fusion bonding
Process
Plural joints
228260, 228 37, 366328, B23K 108, B23K 3102
Patent
active
053682220
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a wavesoldering method for printed circuit boards and to a suitable device for its implementation.
As known, wavesoldering methods and devices provide that the printed circuit boards are conveyed towards one or more waves of molten solder (it is usually used a tin/lead solder melted by means of heating) which "bath" the feet (or the rheophores) of the components laying on the boards as well as the bonding areas therefor arranged. Once the solder is cold, the feet are soldered to the surface of the boards.
In the wavesoldering field, the reduction of the scruffs is a very important problem. In fact, scruffs reduce worse the soldering quality and must be removed from time to time, thereby reducing the productivity of the soldering device. The above problem, well known to the skilled artisan has been solved by making the soldering wave as flat as possible and by limiting the height of the jump of the molten solder.
The coming of the surface mounting components (known as "SMD") has caused some technical problems which are known in the relevant art as "dry soldering" or as "solder skips". The method and the device according to the present invention are hereinafter described referring to the soldering of SMD units by means of a single wave device, but it can be successfully used for the soldering of any components by means of either a single wave or a double wave device.
The surface mounting units are characterized in that the feet are so shaped as to allow the soldering on the same face of the printed circuit where the components are placed.
The phenomenon known as "dry soldering" occurs when air and/or gas bubbles are trapped between two contiguous components, i.e. near to a component, and inhibit the molten solder from bathing the feet and the bonding areas, even if the component is touched by the wave for a long period of time.
The European Patent Application No. 159.425 describes a plurality of solutions for the problem specified above. The solutions provide molten solder wave progressing in an alternative movement which is oblique in relation to the direction of the printed circuit.
The progressive transverse direction of the molten solder wave allows the removal of air or gas bubbles, by partly reducing the soldering failures due to dry soldering, but raises the scruff formation speed, thereby reducing the productivity of the soldering device.
The transverse movement of the molten solder wave is positive to the extent of the removal of the air/gas bubbles present on two of the component's sides (front and rear side in relation to the progressing direction of the component/printed circuit); however, air/gas bubbles remain on the other sides of the component.
The European Patent Application No. 203623 shows a first solution to the above soldering problems providing that the flat soldering wave, pointed obliquely with respect to the front sides of the components, has an alternative or an orbital movement, which allows the removal of air/gas bubbles from any of the component's sides only if the components are mounted sufficiently far from each other. No increment of scruffs has been evidenced. If the components are mounted too close to each other, the soldering wave could not go in the bottom of the gaps between two adjacent components, removing all the air/gas bubbles.
It is understood that, at least in the present description, orbital movements means a periodic, circular or elliptic movement made by a rigid body (as, for example, the body 15 of FIG. 4) due to the rotation of one or more cams or to the movements of corresponding mechanical devices.
The present invention refers to a soldering method and to a soldering device suitable to remove the air/gas bubbles from any of the component's sides, even if the components are mounted on the printed circuit very near one another, thereby avoiding soldering failures due to "dry soldering" and improving the previous soldering methods and devices known, for example, EP-A-203623.
Object of the present invention is theref
REFERENCES:
patent: 1572306 (1926-02-01), Northcutt
patent: 4540114 (1985-09-01), Pachschwoll
patent: 4547076 (1985-10-01), Maurer
patent: 4684056 (1987-08-01), Deambrosio
Bradley P. Austin
Italtel Societa Italiana Telecommunicazioni S.p.A.
Knapp Jeffrey T.
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