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Pink ring is a ubiquitous problem arising during the manufacture of multilayer PCBs, being the manifestation of local delamination at the inner‐layer oxide interfaces around drilled holes and subsequent dissolution of the oxide during plating processes. Except in extreme cases, there is no evidence that the occurrence of pink ring identifies any in‐service reliability problem, but it is nevertheless a clear process indicator and is strictly monitored in statistical process control. The UK Printed Circuit Industry has carried out a collaborative research programme aimed at providing an understanding and a quantitative analysis of the pink ring condition. The research has advanced on two fronts: (i) an investigation into the micro‐mechanisms of the delamination and stress relief around drilled holes and subsequent rôles of the desmear and plating chemicals, and (ii) a statistical analysis of boards manufactured in a variety of ways, analysing the quantitative measurements of pink ring in terms of, for example, panel source, drill supplier, drill quality, drilling backing material, drilling chip rate, stack position, and panel entry/exit side.

For a given batch of printed circuit boards of a particular quality and with a particular level of moisture absorption, the parameters of a wave soldering machine may be tuned to minimise the amount of visible blowholing. This paper shows the inter‐relationships of blowholing with other soldering faults such as icicling, bridging and poor pull‐through. The inter‐relationships result from adjusting each machine parameter in turn. This is important since blowholing cannot be minimised without regard to these other effects. The effect of the quality of the printed circuit boards on the response to machine parameters is predicted from a model, and measurements are found to be in agreement with the predictions.

There is a reliability concern in the larger plastic surface mounting packages which can exhibit cracks from internal stresses during soldering. A lot of ad hoc information has been given to users of such packages about the origins of the problem and its alleviation. The phenomenon is the result of a combination of moisture absorbed in the plastic and the thermal stresses caused by the different expansions of the metal leadframe and the plastic. The work reported here gives quantitative data regarding the amount of moisture absorption critical to cracking, the range of baking procedures available to reduce this moisture below the critical level, and the acceptable floor life after baking for a wide range of storage temperatures and humidities.

In this study, the reliability of solder joints and plated‐through hole copper pads/barrels of pin grid array assemblies under rework condition has been determined by fatigue experiments. The cross‐sections of the re‐worked PGA assemblies (before and after fatigue tests) are also provided for a better understanding of the failure mechanisms of the composite structure. Furthermore, the load‐drop curves of the PGA interconnects for up to three reworks are provided for a better estimate of their fatigue life.

The amount of gas blowing into the molten solder in plated‐through‐holes during wave soldering is dependent upon the moisture content of the board and the strength of the copper barrels to withstand the pressure of gas. This strength is dependent, in turn, upon both the thickness of the copper electroplate and the quality of the original electroless copper deposit. The problem of blowholing may be overcome by improving the copper quality and/or by baking the PCB prior to soldering. This paper gives a scientific framework linking the important parameters involved in the control of blowholing. Full data are given to enable the allowable moisture content of a PCB to be calculated in respect of the pressure generated during soldering and of the strength of the copper barrels. If baking is required to attain the required low moisture levels, then certain data are required to quantify the effects of the storage times and the environment conditions between that bake and the subsequent soldering. These data are given.

This is the third paper in the series of eight, studying voids and blowholes in PTH printed circuit boards. In the previous papers the industrial significance of this problem has been established and moisture identified as the primary cause of the gassing. Now, particular attention is focused on the understanding of the mechanisms and kinetics of moisture uptake in the FR‐4 laminate. From the authors' data the rate of moisture uptake and the rate of drying of laminate can be predicted as a function of temperature and relative humidity.

One family of defects in soldered electronic assemblies that is almost invariably re‐worked is that due to outgassing, manifested as visible blowholes and solder blow‐out. It is known that re‐working can be very detrimental to the service life of an electronic assembly and should be avoided whenever possible. This paper describes work aimed to determine whether outgassing faults such as blowholes are harmful to service performance or whether more harm will be done by re‐working such faults. Standard test plated‐through‐hole (PTH) assemblies with controlled degrees of outgassing faults have been subjected to mechanical testing, thermal shock testing, mechanical fatigue, low cycle thermal fatigue and corrosion testing. Measurements in all these régimes have been carried out quantitatively with baseline controls. No evidence of significant loss of solder joint performance has been found, even for severe cases of solder loss. On the contrary, in cyclic fatigue testing, solder fillets with outgassing faults exhibit statistically significant performance enhancement. The conspicuous nature of blowholing and solder blow‐out undoubtedly over‐emphasises the problem during visual quality control inspection. Provided the copper barrel has been wet by the solder, outgassing faults should not be re‐worked. These faults should be used as process indicators and to draw attention to processes and the need for process control.

This paper is the second of a series dealing with the blowholing problem on through‐hole plated printed circuit boards. In the previous paper the authors have considered the impact of the problem on the UK electronics assembly industry. Here they consider the nature of the gas causing blowholes and voids, its origin and the kinetics of its generation and evolution. When a printed circuit board with plated‐through‐holes is wave soldered, the thermal spike of the molten solder activates the evolution of gas, sometimes in relatively enormous quantities. The gas is seen bubbling from the surface of the molten solder in the joint. Upon freezing, the solder either traps the gas in a void enclosed within the fillet or, if the gas is escaping from the surface as freezing occurs, forms a blowhole.

This paper introduces a series of eight describing the research work undertaken into the most pervasive of quality assurance problems in the mass soldering of plated‐through‐hole (PTH) printed circuit boards, namely the occurrence of voids and blowholes in the solder fillets. The research programme has been carried out at NPL with advice and practical involvement of members of the Soldering Science and Technology Club whose contributions have played a large part in its successful outcome. The work has led to an understanding of the mechanisms giving rise to this problem and recommendations for production procedures to fully control it. In this first paper, results are presented of a UK‐wide survey of the electronics assembly industry and of the assessment made regarding the extent, the harmfulness and the cost of the problem of voids and blowholes.