Circuits Assembly - November 2007 - (Page 52)

Wave Soldering General Settings for a Wave Process Machine and product aspects must fit to ensure the best joints. uestions often arise as to recommended wave wave height of 6-8 mm is the best setting. Lower setsoldering settings, or if general setting data tings may permit component movement during solcan be provided. An important aspect in dering, as the leads may touch the nozzle rim. A wave wave soldering is that all joints, in principle, will get setting should be constant within a few tenths of a the same dwell time. This means joint designs must millimeter. For this reason also, the pot’s solder level be such that they all can provide a sound joint; the should be monitored and corrected automatically. surface and thermal solderability, and the layout of The correct setting of a chip wave or smart all joints to be soldered, must be in accordance with wave depends on the SMD layout and if the board the process used. Only when these basic requirehas slots or large apertures through which this ments are met can one wave may penetrate to run a sound process. the top side of the board. Conveyor speed, If only low wave settings conveyor angle, contact can be used, it might be length, fluxing, preheatnecessary to reduce the ing, solder temperature, conveyor speed to avoid solder alloy, exhaust and skipped joints. nitrogen use are machineConveyor speed. A related aspects. Board general conveyor speed type, thermal aspects, setting is in the range solder resist, SMDs, of 1-1.5 m/min. (17-25 board layout, bending mm/s). The speed setof the board, and palting depends on the let use are product-relatboard type. Single-sided aspects. All aspects ed boards can often be together must make the Figure 1. Bridging (at left) is a common solder-oxide soldered at high speed, related defect. right fit, especially since since they often have a wave-soldering machines low thermal demand for use different settings and recipes. the joint formation. Conversely, a multilayer PCB Process boundaries. A board must be touched by may have such a high thermal demand for the joint the solder wave for a sufficient time to make a good formation that 1 m/min. is even too fast. The layout joint. The board may not enter the wave at such a of the joints on the solder side can be a decisive depth that the solder will flow over the top side of factor in the speed setting, in order to promote the board. To fulfill these requirements, the solder optimal separation conditions to prevent solder wave setting must be such that the top of the solbridging. der wave crest is half the board thickness, or about Fluxer. The spray fluxer setting is related to the 1 mm lower than the top side of the board in the conveyor speed. Important aspects include applicaconveyor. tion of the correct amount of flux. How much flux Contact length. With a conveyor angle of 7°, the should be applied can be found in the flux supcontact length of the main wave on a glass plate plier’s datasheets. Next, one must measure the flux at the same level as the board will be about 25 flow with different settings, because the general mm. The real contact of a joint in the solder wave data in the machine manual are just general. It is depends also on the protruding length of the leads important to control the flux volume; too much at the solder side, and on the board layout. This real may interfere with the soldered product’s electricontact length can therefore be twice as much. This cal reliability, depending on the board application is important to know if one checks the actual dwell requirements. time. Some board bending may be permitted, but be Functionally, flux removes oxides from the joints aware that wave height does not permit much bendto be soldered and from the solder wave in contact ing. Boards can often be kept sufficiently flat with a with the board. The flux must also provide a suffiboard support (wire or skate) or with a pallet. cient “tail” activity when the board leaves the wave Wave height. The wave height should be kept low to promote bridge-free soldering. The main issue to avoid too much dross formation. In general, a here is that a correct fluxer setting is of primary Q Ursula Marquez de Tino is a process and research engineer for Vitronics Soltec (vitronics.com); umarquez@ vitronics-soltec.com. 52 Circuits Assembly NOVEMBER 2007 circuitsassembly.com http://vitronics.com http://vitronics.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - November 2007

Circuits Assembly - November 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Better Manufacturing Pb-Free Manufacturing from a Tier III EMS Perspective ‘Living Documents, Subject to Change’ Creating Ideal Solder Joints An Alternative Drying Process for MSDs ‘Customer Satisfaction is More than a Score’ Optoelectronic Substrates: Will They Happen? Tech Tips Wave Soldering Process Doctor Test and Inspection Getting Lean Materials World Equipment Advances Product Spotlight Assembly Insider Technical Abstracts Ad Index

Circuits Assembly - November 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.