Showing papers in "Circuit World in 1980"

Effect of Surface Contamination of Copper, Arising from Water Rinsing on Solderability

Abstract: Rinsing treatments on copper after etching are investigated by using the adverse effect they have on solderability. The wetting time, as measured by the GEC Meniscograph, is a sensitive indicator of the effect of varying contact times with water (the most obvious way of removing etching residues). Several variables of the water were examined such as dissolved impurities (as indicated by a comparison of demineralised, boiled demineralised and tap‐water) rinsing time in tap water and water temperature. Wetting time is found to rise with all of these and demineralised water is superior to tap water, as might be expected. Very small amounts of acid added to the rinsing solution appear to retard almost completely the contamination effects of the water. All the findings underline how important surface cleanliness is to a successful soldering operation. By corollary it appears that solderability tests (especially the GEC Meniscograph) are very good indicators of extremely low levels of surface contamination.

Evaluation of Drilled Hole Quality as a Function of Speed and Feed in Multilayer Boards

Abstract: Studies of the drilling process have shown that a direct correlation exists between the quality of a drilled hole and the energy expended by the drilling system in forming the hole. As the drilling energy increases (for a given board and drill) the quality of the hole decreases. Hence drilling energy can be used as a measure of drilled hole quality. A drilling energy monitor which can evaluate drilled hole quality on line is being used to investigate several aspects of the drilling process. One of these studies, the effect of feed‐rate and spindle speed on drill performance is the subject of this paper. Drilling energy as a function of drill age has been investigated at several combinations of feed‐rate and spindle speed. No. 56 drills were aged in 8 layer multilayer boards for up to 3000 holes while monitoring the drilling energy. Spindle speed was varied between 60 and 300 inches per minute. It was found that the rate of increase of drilling energy is lower for drills worn at a high advance per revolution than for drills worn at a low advance per revolution. Longer drill life can be obtained by drilling at a high advance per revolution. Spindle speed had little effect on the rate of increase of drill energy over the range of feed and speed used in this study. This paper presents the experimental data and makes recommendations on the proper usage of No. 56 drills.

I/C Packaging and Interconnection Developments

Abstract: This paper describes the major new I/C packaging technologies now coming into use, i.e., chip carriers and tape automated bonding. It deals with the reasons for their development, where they are most likely to be used and their impact on current interconnection technologies, i.e., PCBs and thick film hybrids. The paper also looks briefly at some new developments in ‘off‐the‐chip’ interconnection, e.g., laminates and materials.

Soldering and Fusing by Condensation Heat Transfer

Abstract: When saturated vapour condenses to liquid, latent heat of vapourisation is released to the item causing the condensation, this item which is itself heated. Use is made of this natural phenomenon in order to melt solder alloys melting below 216°C in a relatively new process known both as Condensation Soldering and Vapour Phase Soldering. Solder joints of the conventional type can be produced by using condensation heating to melt strategically placed preforms or solder creams and very many joints are produced simultaneously in correctly designed equipment. Plated tin‐lead coating on printed circuit boards can also be successfully fused, in some instances without application of external fluxes. Advantages over existing heating processes include geometry independent heating, oxygen‐free environment, absolute temperature control, excellent chemical compatability, absence of residues and very high heating rates. Major benefits can include operator independence, extremely low joint cost combined with excellent joining reliability both leading to greatly reduced re‐work and consequent improvement in quality and economies. There are presently about 150 facilities operating in the USA and about ten in the UK. Many tens of millions of joints are produced each year in this way with joint costs as low as 0.03 cents and reject rates less than 0.2%

The Use of the Laser for the Inspection of Printed Circuit Boards and Laminates

Abstract: Scanned Helium‐Neon laser beams are finding increasing use for non‐contact industrial inspection applications where high resolution detection of optical properties of materials and components is required.

Measuring the Thickness of Coatings on Printed Wiring Boards

Abstract: The Beta Backscatter Coating Thickness Gauge has been a very well used “tool” in printed wiring production for many years. The increased requirement to more closely control the quality and cost of high priced materials and processes has been met by instrument developments utilising microprocessors, not only for measurement but also for instrument, operator and results evaluation. Despite this, the instrumentation will only deliver the correct results if given correct information in the first place, thus, the operator must know a little of the preceeding coating process or at least be given the relevant and correct information. This paper describes the importance of the substrate material and the density of the coating material when measuring coating thickness.

Optimum Design of Flexible Printed Circuit Boards with Respect to Flexural Strength

Abstract: In the course of flexible PCB manufacture where the reliability of those parts subjected to bending stresses is a matter of utmost concern, the design of the PCB should enable the flexible interconnection parts to withstand the greatest possible bending stresses. Therefore, extensive investigations were carried out to demonstrate the relationship between the design and flexural strength. The study shows the functional correlation between bending radius, material thickness, type of material, design of the circuit and number of bending cycles. Only with a detailed knowledge of these five mentioned properties can reliable PCBs be designed and manufactured. The results of these investigations are based on a great number of bending experiments performed on a practical basis and demonstrate the numerical relation between all effects. As bending cycle results are subject to relatively high deviations, the whole problem has been investigated by means of statistical evaluation criteria.