Pb-free PTH rework on a thick, heavy assembly: a forced convection platform with a solder fountain showed a dramatic impact on copper dissolution.Benchmark Electronics conducted a Pb-free implementation for a customer in January January: see month. 2006 that included documentation of the process and findings by the Toxic Use Reduction Institute. (1,2) This customer designs and manufactures computer systems based on open industry standards. The Pb-free conversion was done on a limited number of an existing SnPb high-reliability medical product. This product is referred to as the Maverick Maverick family name of two brothers, Bret and Bait; self-centered and untrustworthy gentlemen gamblers. [TV: Terrace, II, 80] See : Gambling Card and is 7.5" by 9.2", 16 layers with seven layers being power or ground, 0.084" thick, and populated pop·u·late tr.v. pop·u·lat·ed, pop·u·lat·ing, pop·u·lates 1. To supply with inhabitants, as by colonization; people. 2. with a total 1,694 SMT (1) (Surface Mount Technology) See surface mount. (2) (Station ManagemenT) An FDDI network management protocol that provides direct management. Only one node requires the software. SMT - Station Management and PTH PTH abbr. parathyroid hormone Parathyroid hormone (PTH) A chemical substance produced by the parathyroid glands. This hormone is a major element in regulating calcium in the body. components on both sides. The SnPb version has been in production for an extended period of time. The Pb-free version included three surface finishes: OSP (Online Service Provider) See online service. OSP - Optical Signal Processor , ENIG ENIG Electroless Nickel Immersion Gold (printed circuit board manufacturing process) and ImAg; all chemistry was organic acid (OA). The assembly required four reflow (1) The process of heating and melting the solder that has been screen printed onto a printed circuit board in order to bond chips and other components to the board. Surface mount chips (SMT) use the reflow method. Contrast with wave soldering. See also reflowable text. cycles because select BGAs could only be obtained as SnPb. The four assembly profiles were, in order, Pb-free bottomside, Pb-free topside, SnPb bottomside and SnPb topside. All PTH components were soldered Pronounced "sod-erd." Permanently attached by a hard metal bond. In order to replace a chip soldered to a circuit board, it requires heating the soldering joints until they melt. Contrast with socketed. during the original assembly on a SAC Sac: see Sac and Fox. SAC - 1. An early system on the Datatron 200 series. [Listed in CACM 2(5):16 (May 1959)]. 305 solder solder (sŏd`ər), metal alloy used in the molten state as a metallic binder. The type of solder to be used is determined by the metals to be united. Soft solders are commonly composed of lead and tin and have low melting points. Hard solders (i. fountain fountain, natural or artificially conveyed flow of water. In ancient Greece columnar shrines were built over springs and dedicated to deities or nymphs. In ancient Rome fountains fed by the great aqueduct system furnished water in the streets, in the villa gardens, with the molten solder at 285[degrees]C. The solder fountain included complete board preheat pre·heat tr.v. pre·heat·ed, pre·heat·ing, pre·heats To heat (an oven, for example) beforehand. pre·heat  er n. to a topside laminate laminate,n a thin slice of porcelain or plastic fabricated in a dental lab, which is cemented to the front of the teeth to cover gaps, whiten stained teeth, or reshape chipped or broken teeth. temperature of 132[degrees]C prior to component soldering soldering Process that uses metal alloys with low melting points to join metallic surfaces without melting them. Tin-lead solders, once widely used in the electrical and plumbing industries, are now replaced by lead-free alloys. . The average contact time on the solder fountain was 9 sec. for each PTH component, and the objective was to obtain IPC-A-610 Class 3 joints during the original assembly and subsequent forced rework re·work tr.v. re·worked, re·work·ing, re·works 1. To work over again; revise. 2. To subject to a repeated or new process. n. . Class 3 joints require a minimum of 75% flow solder fill in the z-axis. PTH Forced Rework Practice Boards 1 and 2 were selected for development work prior to reworking a PTH component on the Maverick Card. The objective: Identify the optimum rework method to achieve IPC (1) (InterProcess Communication) The exchange of data between one program and another either within the same computer or over a network. It implies a protocol that guarantees a response to a request. Class 3 through-hole joints with minimal copper dissolution Act or process of dissolving; termination; winding up. In this sense it is frequently used in the phrase dissolution of a partnership. The dissolution of a contract is its Rescission by the parties themselves or by a court that nullifies its binding force and reinstates each , pad lifting and laminate thermal degradation DEGRADATION, punishment, ecclesiastical law. A censure by which a clergy man is deprived of his holy orders, which he had as a priest or deacon. . Single, double and triple reworks were evaluated. A single rework is defined as removal and replacement of a PTH component; a double rework is the second removal and replacement of the component at the same site. The board is permitted to cool to room temperature between rework cycles, and a triple rework follows similarly. Double and triple reworks on the same site would be rare in practice, but a successful double rework may be necessary and also provides a higher confidence level for the integrity of a single rework. Practice boards 1 and 2 were identical and selected because they had an OSP surface finish, which has a significant risk of copper dissolution. Moreover, the boards had 10 sites for the same PTH component, which permitted different techniques to be assessed at various board locations. The sites were sufficiently apart to minimize the thermal impact of rework from adjacent sites. The board was 14.5" by 16.5", 0.074" thick, and four of the 10 layers were power or ground. Figures 1 and 2 (online) show the practice board and respective component. [FIGURE 3 OMITTED] [FIGURE 6 OMITTED] Practice board 1. Sites 1 through 4 on practice board 1 were reworked completely on a SAC 305 fountain set at 280[degrees]C. The original component installation was performed on the same solder fountain. All reworked boards were preheated to a topside temperature of 150[degrees]C and subjected to single or double rework. The rework nozzle An orifice in an inkjet print head through which ink is sprayed onto the paper. Print heads with six thousand or more nozzles are common in today's printers. Nozzle style was varied to provide a "stagnant stagnant /stag·nant/ (stag´nant) 1. motionless; not flowing or moving. 2. inactive; not developing or progressing. " or "full flow." Stagnant flow is defined as solder making intimate contact with the board's bottomside, but not overflowing o·ver·flow v. o·ver·flowed, o·ver·flow·ing, o·ver·flows v.intr. 1. To flow or run over the top, brim, or banks. 2. To be filled beyond capacity, as a container or waterway. 3. the sides of the nozzle. Full flow is defined as solder making intimate contact with the board's bottom and overflowing the sides of the nozzle. The objective was to determine if stagnant flow reduced copper dissolution as compared with full flow. The rework contact time is defined as the period the solder makes intimate contact with the board bottom. The flux flux In metallurgy, any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores. used was Vendor A OA flux paste. [FIGURE 7 OMITTED] [FIGURE 8 OMITTED] [FIGURE 9 OMITTED] Figure 3 shows a summary of the results. The digit A single character in a numbering system. In decimal, digits are 0 through 9. In binary, digits are 0 and 1. digit - An employee of Digital Equipment Corporation. See also VAX, VMS, PDP-10, TOPS-10, DEChead, double DECkers, field circus. in the lower corner of each cross-section corresponds to the applicable site, and each site includes three cross-sections: the complete, top and bottom view. The process summary appears in the right column. PCB PCB: see polychlorinated biphenyl. PCB in full polychlorinated biphenyl Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. copper thickness measurements on Sites 1 through 4 were taken (Figure 4, online, and Table 1). The top layer pad copper is on the board's topside, and masking mask·ing n. 1. The concealment or the screening of one sensory process or sensation by another. 2. An opaque covering used to camouflage the metal parts of a prosthesis. covers the bottom layer trace copper. Both locations have negligible  This article or section is written like a personal reflection or and may require .Please [ improve this article] by rewriting this article or section in an . risk of copper dissolution and can be considered baselines for the original copper thickness. All measurements in Figure 4 are mils. Some observations from the data: * All four sites were acceptable. There was no evidence of excessively thin or fractured Fractured is the Industrial Music band created by Canadian Nick Gorman in 2003. Located in Toronto Canada, his self produced release CD-R demo entitled Contami-Nation caught the attention of European label Dependent Records, who signed them. knees, nor was there any significant via wall thinning near the surface. Copper thickness was above the IPC Class 3 minimum of 0.001". * Copper dissolution increased for the double rework as compared with the single rework, which was expected, but the increase was smaller than anticipated. * The difference in copper dissolution between the stagnant and full flow was not significant. * By the end of the double rework process, the bottomside pads lost approximately one-quarter their original copper thickness, regardless of the method used. [FIGURE 10 OMITTED] Practice board 2. Practice board 2 was used to assess a different rework process in which forced convection was used to remove the connector and vacuum solder from the through-holes. The solder fountain was only used to install the component. This process significantly reduced the contact time on the solder fountain; it was hypothesized this would minimize copper dissolution. One connector location was subjected to a double rework; another connector was subjected to a triple rework; the two sites were referred to as 2X and 3X, respectively. [FIGURE 11 OMITTED] [FIGURE 12 OMITTED] Hot air component removal and hole cleaning parameters were: * Board topside preheat for component removal and hole cleaning: 160[degrees]C. * Peak temperature of the component plastic body: 245[degrees]C. * Peak temperature of solder in barrel: 225[degrees]-235[degrees]C. Component installation on the solder fountain parameters were: * Board topside preheat: 150[degrees]C. * Temperature of the solder: 280[degrees]C. * Contact time: 8-9 sec. PWB (Printed Wiring Board) An alternate term for printed circuit board. See printed circuit board. copper thickness was measured (Figure 5, online, and Table 2). The top layer pad copper is on the board top; masking covers the bottom pad copper. Both have negligible risk of copper dissolution and can be considered baselines for the original copper PWB thickness. All measurements are in mils. The measured results were acceptable for 2X and 3X reworks per IPC Class 3 criteria. The copper thickness at the knees did not go below 0.001", and the amount of copper dissolution on 2X and 3X reworks was equivalent, which was somewhat surprising. It was anticipated the dissolution would increase on the 3X rework as compared with the 2X. The final copper thickness on the bottom pad copper and knee copper were less on practice board 1 as compared with practice board 2, which was not anticipated because the solder fountain contact time on practice board 2 was lower. However, based on the copper thickness of the top layer pad copper and bottom layer trace copper, it appears practice board 1 had more copper prior to the start of the rework as compared with practice board 2, and this would explain the results. Figure 6 shows cross-sections of the 2X and 3X rework. The 2X or 3X figure in the lower part of the image denotes the respective rework. The 2X and 3X rework cross-sections were acceptable per IPC Class 3 criteria. Copper dissolution was acceptable, and the small amount of pad lifting is consistent with SnPb through-hole rework. Solder flow-through to the topside was 100%; there was minimal voiding; wetting was good, and there was no laminate thermal degradation. Maverick Card PTH Rework The Maverick Card is 0.084" thick, 16 layers with 7 ground/power planes. Compared to practice boards 1 and 2, it represents a significantly more difficult rework challenge in terms of thermal load. The component selected for rework on the Maverick Card was the 16-pin header (1) In a disk or tape file, a set of data that resides permanently at the beginning. It may be used for identification only (type of file, date of last update, etc.), or it may describe the structural layout of the contents, as is common with many document and database formats. at Location J6. The Maverick Card and the header at Location J6 appear in Figures 7 and 8. Maverick Card 3 -- OSP surface finish, double rework on the solder fountain. Practice boards 1 and 2 results indicated a double rework done completely on the solder fountain would be successful. It was decided to employ this process on Maverick Card 3, which had an OSP surface finish. This process is faster as compared with the alternative forced convection process because it takes less time to remove a component on the solder fountain as compared with the forced convection platform. The solder fountain parameters for the rework of the 16-pin/header at Location J6 on Maverick Card 3 were: * Topside board preheat temperature: 150[degrees]C. * SAC 305 solder temperature: 280[degrees]C. * Contact time for each rework: 20 sec. * Total contact time for both reworks: 40 sec. * Flux: Vendor B flux paste. Contact time for each rework is defined as the total time required to remove a component and install a new one while the solder is making continuous contact with the board bottom. The contact time for the original assembly was 9 sec., which means the total contact time for assembly and rework was 49 sec. Cross-section results are shown in Figure 9. [FIGURE 13 OMITTED] The double rework was not acceptable because of the fractured knee caused by copper dissolution because of excessive contact with the molten SAC 305 solder. This is a known risk with Pb-free SAC 305 rework and has been documented. (3,4) This board would have to be scrapped, which could have significant cost and delivery implications. It should be noted that the fractured knee could not be detected with visual inspection and required destructive cross-sections to see it. The board also exhibited through-hole pull away, which is not acceptable and exhibited undesirable pad lifting. The Maverick Card is a more thermally massive card as compared with the practice boards and required longer contact times on the solder fountain, which likely caused the unacceptable copper dissolution. Maverick Card 4 -- ImAg surface finish, single rework using forced convection in conjunction with the solder fountain. Based on the unacceptable results for the double rework of Maverick Card 3 on the solder fountain, it was decided to perform a single rework incorporating the forced convection platform for component removal and through-hole cleaning in conjunction with the solder fountain. The solder fountain was used only to install the new component, which significantly reduced contact time on the fountain, which in turn minimized the copper dissolution risk. Initially, the forced convection parameters were identical to practice board 2, but the plastic body of the 16-pin header melted melt v. melt·ed, melt·ing, melts v.intr. 1. To be changed from a solid to a liquid state especially by the application of heat. 2. , and it was determined that the plastic was only rated to 220[degrees]C, which made it difficult to remove the component. The topside preheat of the board was increased to 180[degrees]C from 160[degrees]C; the peak temperature on the plastic component body was lowered to 220[degrees]-230[degrees]C, and the component was removed from the board just before the plastic body melted. The PTH solder temperature was 220[degrees]-225[degrees]C. The solder fountain was used to install the new component with the following parameters: [FIGURE 14 OMITTED] * Topside board preheat temperature: 150[degrees]C. * SAC 305 temperature: 280[degrees]C. * Contact time for installation: 9 sec. Cross-section results are shown in Figure 10. The single rework was successful in minimizing copper dissolution, but induced induced /in·duced/ (in-dldbomacst´) 1. produced artificially. 2. produced by induction. induced, adj artificially caused to occur. induced induction. some PCB thermal degradation, as manifested by pad lifting and hole pull away. The pad lifting varied from none to a maximum of 0.002", as seen in the two bottom images of Figure 10. The hole pull away was less than 10% along the entire length. It was believed the thermal degradation was most likely caused by the high topside preheat (180[degrees]C) in conjunction with the time required at this temperature to reflow the component, remove the component and vacuum the holes. The high PCB preheat temperature was required to minimize melting of the plastic PTH component body; a lower preheat would have been used had the PTH component been rated to a higher temperature. A contributing factor was likely the four reflow cycles required during the original assembly, which, in order, were bottomside Pb-free, topside Pb-free, bottomside SnPb and topside SnPb. Maverick Card 9 -- OSP surface finish, double rework with forced convection in conjunction with the solder fountain. Based on the generally positive results with Maverick Card 4, it was decided to conduct a double rework using the same technique on an OSP Maverick Card. The forced convection and solder fountain parameters were identical to Maverick Card 4, and the total contact time on the solder fountain was 18 sec. (two installations). The card selected was Maverick Card 9. Cross-section results appear in Figures 11,12,13 and 14. [FIGURE 15 OMITTED] The process dramatically reduced copper dissolution as compared with the process used for Maverick Card 3. The solder fill was greater than 75% as required for IPC-610 Class 3; wetting was good and voiding was minimal. Slight pad lifting was detected, likely related to the high PCB preheat temperature required to compensate for the low temperature rating of the 16-pin header. Also, this card was subjected to a double BGA (Ball Grid Array) A popular surface mount chip package that uses a grid of solder balls as its connectors. Available in plastic and ceramic varieties, BGA is noted for its compact size, high lead count and low inductance, which allows lower voltages to be used. rework prior to through-hole rework, and the card was reflowed four times during the original assembly. The increased number of thermal cycles was likely a factor in thermal degradation. Standard Pb-free boards would be reflowed only twice during the original assembly; it is unlikely four reworks would be performed on the same board. Maverick Card 8 -- ENIG surface finish, double rework with forced convection in conjunction with the solder fountain. The double rework technique used for Maverick Card 9 was used for Maverick Card 8, which had an ENIG surface finish. Figure 15 shows the cross-section. The joint meets IPC Class 3 Criteria, but there is evidence of slight pad lifting, which is not preferred. The thermal degradation was likely caused by factors similar to those in Maverick Card 9. Copper dissolution on Maverick Card 8 was not an issue, as anticipated given the ENIG PCB surface finish. Conclusions The forced convection platform, in conjunction with the solder fountain, dramatically reduced the copper dissolution observed on the Maverick Card as compared with the rework done completely on the solder fountain. The former is the recommended rework process for thermally massive cards such as the Maverick Card. Overall, the Pb-free through-hole rework processes evaluated were successful. The solder fountain, or a combination of forced convection and solder fountain, is a viable process; optimum rework process selection should be predicated on board design and construction. Additional optimization optimization Field of applied mathematics whose principles and methods are used to solve quantitative problems in disciplines including physics, biology, engineering, and economics. is required to minimize pad lifting. All components should be rated for the higher temperatures associated with Pb-free assembly and rework. The 16-pin PTH header reworked on the Maverick Card was rated to 220[degrees]C and melted during forced convection removal. A 260[degrees]C temperature rating is recommended for all Pb-free components. References 1. Gregory Morose mo·rose adj. Sullenly melancholy; gloomy. [Latin m  r , Richard Russo
Richard Russo (born July 15 1949) is a Pulitzer Prize-winning American novelist. Born in Johnstown, New York, and raised in nearby Gloversville, he earned a B.A. (1967), a M.F.A. , Robert Farrell and Scott Mazur, "Transition to Lead-free Electronics--Case Study," IPC/Jedec International on Lead Free Electronic Components and Assemblies, August 2006. 2. Robert Farrell, Paul Bodmer, Richard Russo and Gregory Morose, "Transition to Lead Free Electronics Assembly Case Study--Part II--Product Reliability and Forced Rework," IPC/Jedec Global Conference on Lead Free Reliability and Reliability Testing for RoHS Lead Free Electronics, April 2007. 3. Craig Hamilton Craig Peter Hamilton (born: 1st September 1979) is a Scottish international rugby union player, playing as a lock. He was born in Dumfries, currently plays for the club rugby for the Glasgow Warriors, is 6 feet 8 inches tall and weighs 17 stones 8 pounds. , Matthew Kelly For the musician associated with Ratdog, Kingfish, and T-Bone Walker, see . Matthew Kelly (born, 9 May 1950, Urmston, Lancashire, England) is an English actor, who made his name as a television presenter. and Polina Snugovsky, "A Study of Copper Dissolution During Pb-free PTH Rework Using a Thermally Massive Test Vehicle," CIRCUITS ASSEMBLY, May 2007. 4. L. Ma, A. Donaldson, S. Walwadkar and I. Hsu, "Reliability Challenges of Lead Free (LF) Plated-Through-Hole (PTH) Minipot Rework," IPCUedec Global Conference on Lead Free Reliability and Reliability Testing for RoHS Lead Free Electronics, April 2007. Acknowledgments The authors would like to thank George Blais Jr, Dorothy Martin, Eduart Pengu, Rosemarie St. Laurent, and Beatrice Sybert of Benchmark Electronics for their assistance performing the rework, analyzing the boards and contributing to this paper. Robert Farrell is principal engineer, Paul Bodmer is principal engineer--product assurance laboratory engineer and Bruce Bruce, Scottish royal family descended from an 11th-century Norman duke, Robert de Brus. He aided William I in his conquest of England (1066) and was given lands in England. Tostevin is senior component engineer, Benchmark Electronics (bench.com); robert.farrell@bench.com. Richard Russo is principal manufacturing process engineer at Mercury Computer Systems Mercury Computer Systems, Inc. NASDAQ: MRCY provides high-performance embedded, real-time digital signal and image processing solutions. Mercury designs and builds embedded multicomputers, which may be considered to be either loosely coupled (mc.com). Gregory Morose is research project manager at Massachusetts Toxics Use Reduction Institute “TURI” redirects here. For other uses, see TURI (disambiguation). “Toxics Use Reduction Institute” redirects here. For other uses, see Toxics Use Reduction Institute (disambiguation). (turi.org).
Table 1. PWB Copper Thickness, Practice Board 1
Site 1 Site 2 Site 3 Site 4
Single Single Double Double
Rework Rework Rework Rework
Stagnant Flow Full Flow Full Flow Stagnant Flow
Top layer pad copper 2.279 2.071 2.701 2.138
Bottom layer trace 2.306 2.216 2.257 2.104
copper
Bottom pad copper 1.996 1.688 1.620 1.564
Knee copper 1.575 1.379 1.305 1.238
Table 2. PWB Copper Thickness, Practice Board 2
2X 3X
Top layer pad copper 1.874 1.764
Bottom layer trace copper NA 2.103
Bottom pad copper 1.357 1.364
Knee copper 1.001 1.035
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