That's not exactly what I said, the question was " I would like to know if HASL plating creates a planarity problem for QFPs or BGAs assembly for some people in the industry." I responded with yes, it creates problems! Can HASL be correctly applied down to tight pitch features (my definition of tight pitch is 10 mils or less), of course! But there are many variables on both sides of the wall that should be addressed first, for example, air/dwell time during the HASL process removing as much solder from the flat pads but allowing just enough to remain behind as to provide the solderable surface, possible stencil adjustments, paste application (to adjust for minimal solder and stencil thickness adjustments), then there may be the type solder to use (as the extreme minimal solder on the bare board may invariably require a different temperature setting during assembly), what type flux is being used, would this interfere instead of enhance the fusing of the board and paste...and the list here may be long. The list above contains many of the variables of why it does not work...of course... Can it be done, sure, but the cost associated with this as well as the potential for low yields make alternative (i.e immersion tin) finishes a better choice. Franklin -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon Sent: Wednesday, October 12, 2005 12:40 PM To: [log in to unmask] Subject: Re: [TN] Hasl Frank: Your are telling me that HASL final plating can be used on most components including fine pitch if they are design in properly and the assembly is done by skilled people and six more variables are correctly done. Is this right? Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard Sent: Wednesday, October 12, 2005 1:29 PM To: [log in to unmask] Subject: Re: [TN] Hasl Like Chinese fireworks and printed circuit boards. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin Asbell Sent: Wednesday, October 12, 2005 12:25 PM To: [log in to unmask] Subject: Re: [TN] Hasl Is that your question? The answer is yes, for some people it does, but it cannot be blamed solely on HASL, you need to factor the HASL process, the dimensions of components being attached, the skill level of those people and about half a dozen other variables. And just a not on planarity, HASL and planarity go together like Laurel and Costello, Abbot and Hardy, Beer and Firearms... Franklin -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon Sent: Wednesday, October 12, 2005 12:16 PM To: [log in to unmask] Subject: Re: [TN] Hasl Thanks Jeff. Is it from pad to pad or from thickest to thinnest pad areas of the board? I would like to know if HASL plating creates a planarity problem for QFPs or BGAs assembly for some people in the industry. Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jeffrey Bush Sent: Wednesday, October 12, 2005 12:00 PM To: [log in to unmask] Subject: Re: [TN] Hasl We control the thickness from .2 to .9 mils - pad centers. We use a HSL-175 horizontal system. Jeffrey Bush Director, Quality Assurance and Technical Support VERMONT CIRCUITS INCORPORATED 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302 Voice: 802.257.4571.21 Fax: 802.257.0011 http://www.vtcircuits.com -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon Sent: Wednesday, October 12, 2005 9:06 AM To: [log in to unmask] Subject: Re: [TN] Hasl Thanks for your comments Dr Lee. I would like to know from the fabricators what is the range in thickness that they can control on a HASL plating finish. Is it 0.1 to 0.6 mills? From the fabricators what is the finest part pitch that they can assemble on PWBs. Thanks for your inputs. Ramon ME 410.552.2210 _____ From: Lee parker [mailto:[log in to unmask]] Sent: Tuesday, October 11, 2005 8:10 PM To: TechNet E-Mail Forum; Dehoyos, Ramon Subject: Re: [TN] Hasl Ramon Normally, HASL is the less expensive alternative and thinner. Consequently by being thinner, it may produce a smaller meniscus which is usually an advantage. The risk here though is solderability; the thinner the solder the more likely the occurrence of surface intermetallics. These issues have been the focus of engineering attention for years and have become more acute as the feature sizes diminished. This is why the the industry is migrating from HASL to hard metal finishes. Best regards Lee J. Lee Parker, Ph.D. JLP Consultants LLC 804 779 3389 ----- Original Message ----- From: Dehoyos, Ramon <mailto:[log in to unmask]> To: [log in to unmask] Sent: Tuesday, October 11, 2005 4:20 PM Subject: Re: [TN] Hasl Thanks Dr Parker and Richard for your inputs. Comparing SSSR and HASL final plating which are made both using eutectic Tin/Lead solder and other Lead free materials, the end surface is still domed in the middle. So both have weak gasketing due to their lack in flatness. Setting this issue aside, what are the advantages of one versus the other besides the longer shelf life of SSSR. Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard Sent: Tuesday, October 11, 2005 2:03 PM To: [log in to unmask] Subject: Re: [TN] Hasl The idea of the flat surface finish is for both stencil gasketing to the board and for placement accuracy. To form a "perfect brick" of solder paste, there has to be a certain amount of pressure (a lot less than most people think). To prevent squeezout of paste between stencil and board, there has to be good, really good, gasketing or sealing between the stencil and the board surface. The problem with HASL, as Dr. Parker stated below, is that the round bump (meniscus) of HASL sticking up above the surface of the pad on vias and on surfaces where there is no accomodating hole in the stencil prevents this tight seal, and allows the paste to squeeze out. (The aperture design is typically slightly smaller than the pad). It is also a problem when you go back and perform pick-n-place, as now you want to place the SMT components onto your perfectly formed bricks of paste, but with about 50-100 grams of pressure. If the paste is not stable to a flat pad, the parts slide all over the place. While some of this is forgiven by the surface tension of the solder in liquidus, bridges do form, components misalign, etc. This is especially critical in a no-clean process. If large (relatively) amounts of the solder paste are not "tight to the brick" and fully registered on the pad, the paste does not fully agglomerate into a single solder joint. Separated solder paste does not usually conglomerate back into the central solder joint during reflow. Extraneous solder balls form. This is very bad news if you did not plan on washing them away. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker Sent: Tuesday, October 11, 2005 12:03 PM To: [log in to unmask] Subject: Re: [TN] Hasl Ramon After reflowing a soldered surface, you will form a meniscus which will interfere with SMT component placement. To avoid the problem I suggest a flat metal finish such as immersion silver or flash gold (not ENIG) Best regards Lee J. Lee Parker, Ph.D. JLP Consultants LLC 804 779 3389 ----- Original Message ----- From: Dehoyos, Ramon<mailto:[log in to unmask]> To: [log in to unmask]<mailto:[log in to unmask]> Sent: Tuesday, October 11, 2005 12:52 PM Subject: [TN] Hasl Hi technetters: Is there a fine pitch limit to the use of HASL board plating finish due to its variation in thickness? Does selective solder strip and reflow plating, SSSR, have a significant advantage over HASL? Any comments relating to platting finish would be greatly appreciated. I thank you for your comments. 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