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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