Colonial Circuits, Inc. 1026 Warrenton Road Fredericksburg, Virginia 22406-6200 Voice: 800 578 9602 Fax: 800 631 0856 Try this company, they are good. Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei Sent: Tuesday, May 08, 2007 8:16 PM To: [log in to unmask] Subject: Re: [TN] (2) What is the difference between Fused SnPb and HASL? Hello, Thanks so much for all the information. I have need for Fused SnPb finish PCBs that will not have soldermask and silkscreen. Can I have recommendations on which company can support the fabrication to meet my requirement? It is more a prototyping quantity. Regards, Wee Mei ________________________________ From: TechNet on behalf of Barmuta, Michael Sent: Wed 5/9/2007 7:02 AM To: [log in to unmask] Subject: Re: [TN] (2) What is the difference between Fused SnPb and HASL? Hi Richard: I have to take issue with some of your comments. First of all I'm not a proponent of HASL. Secondly, I built fused tin/lead (FTL) boards for over twenty five years so I probably know a little bit about it. Regards Michael Barmuta Staff Engineer Fluke Corp. Everett WA 425-446-6076 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Tuesday, May 08, 2007 1:25 PM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? And in rebuttal, also because fused tin/lead allows a very flat surface without some of the drawbacks of immersion silver, ENIG, OSP, and of course, HASL. A FTL surface is not flat. It suffers from uneven thickness. This is caused by variations in current density during the electroplating of the tin/lead. High current density areas have more plating than the LCD areas. Thus they end up with thicker deposits There are a lot of companies using FTL finish on PWBs, and for very, very good reasons. Although it may cost slightly is a pretty non descript term. I have found if you want FTL without the TL under the mask i.e. with the additional selective masking and stripping it is a 20% adder. IF you can find someone to do it. more than HASL, its application process is much easier on the PWB than HASL, and it can effectively be applied the first time without a bunch of rework, The reason there is not a bunch of rework on a FTL board is you cant rework one, once it's been etched. It can't be re-plated and if it didn't wet to the surface copper during fusing there's nothing you can do to fix it. which is not always true of HASL. As illustrated in all of these postings, FTL is a very misunderstood plating. Properly applied, it does NOT leave tin/lead under the soldermask. The standard FTL process DOES leave TL on the circuitry unless you go thru a process intensive set of masking, stripping and cleaning steps. It does NOT leave copper slivers along the tops of features. It does NOT present a surface that is difficult for soldermask to adhere to. "Why not just build a SMOBC/HASL board?" There are a lot of reasons. First of all, I have yet to see a board house that can consistently, over time, provide HASL boards where the HASL was not reworked at least one time before the boards ever leave the fabricator, and usually it is done many times. If your board supplier has to run back thru HASL many times you've got the wrong board supplier. Evidence of this is manifest in the number of postings on this forum where HASL PWBs were received that could not be soldered properly due to dewetting issues. This is because after a certain number of HASL rework cycles there is so much Cu diffused into the HASL that during the initial soldering processes there is already a high level of dewetting taking place. Secondly, the HASL deposits are extremely non-uniform, As are certain FTL designs. See above on current density. with some areas/pads retaining much more of the HASL solder than others, and very poor gasketing between the stencil and the board occurs. This is the reason other plating methods were looked at as components developed finer pitches, along with the advent of the BGA. Trying to place a component with thin compliant leads less than .020" apart or round balls on top of a pad covered with a single dome of hard solder and covered with thousands of tiny little solder marbles (paste) just does not work very well. It usually leads to bridging and non-uniform paste deposits in both volume and shape on all but the most basic, 50mil-pitch PWBs. Thus the development of ENIG, IAg, OSP, etc., which are all flat finishes. I don't think you'll see much wide spread use of FTL in commercial, industrial, telecommunications, etc. but som how they get it done. FTL is still commonly used, especially in military, avionics, and space programs, by quite a few companies. I would question about it being commonly used. If it was widely used you would find a lot more shops offering it. I don't have the number but I would guess it is very small percentage of all boards fabricated world wide. Like any other finish, your successwith it is directly dependent on the performance of the board fabricator who applies it. Properly done, it can be one of the best, most reliable finishes you can possibly solder to. And just like you said, Ramon, it works. Yes but at a definite $cost penalty that's why you see it still being used in military, avionics and space. They don't care what the price is and are still running on 30 year old drawing and call outs. FTL provides excellent solderability, without all of the harshness and variability and stresses to the PWB present with HASL. FTL has it's own issues on harshness, variability and stresses. The boards are normally run thru a heat cycle such as an IR oven to melt the co-deposited electroplated TL. Ask someone from the military how they like their high frequency Teflon multilayer board run thru the fuser. That's why they use not melting final finishes I am not saying HASL has no place, either. There are different finishes, all have their strengths and drawbacks. HASL is simply not my first choice as a surface finish when I am determining what to use for the guidance system of a nuclear missile, a flight control computer, an airport tower communications system, or a traffic control system for a high-speed train, for example. I would certainly feel comfortable designating FTL if the design warranted it, however. Selective FTL has its place if you really need it and want to pay for it but I see it as a dying technology that will have limited availability. A dinosaur of the past, living on due to ghosts walking the hall. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon Sent: Tuesday, May 08, 2007 1:47 PM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Hi Michael: HASL is much less expensive and less time consuming to plate. Selective solder reflow is used by very few companies that are not ready to change the way things were made long time ago just because it works. Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, Michael Sent: Tuesday, May 08, 2007 11:37 AM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Hi Ramon: As I said "conventionally built" fused Sn/PB boards have the fused Sn/Pb on the circuitry under the mask. This is how standard fused Sn/Pb board were built in the 60's, 70's and beyond. A more unconventional approach is what you are referring to. Boards can be built this way but are more complicated and expensive due to the additional processing. However it will take care of the melting metals under the mask condition. If you are going to go to all the trouble of maintaining a Sn/Pb plating line, plating Sn/Pb, selectively masking, selectively stripping the plating, stripping the masking, fusing, washing, cleaning the exposed Cu, applying soldermask, etc, why not just build a SMOBC/HASL board. It's much simpler. Regards Michael Barmuta Staff Engineer Fluke Corp. Everett WA 425-446-6076 -----Original Message----- From: Dehoyos, Ramon [mailto:[log in to unmask]] Sent: Tuesday, May 08, 2007 7:37 AM To: TechNet E-Mail Forum; Barmuta, Michael Subject: RE: [TN] What is the difference between Fused SnPb and HASL? Michael: Traces or other geometries that are not to be soldered and are going to be under the solder mask do not need to have fused solder at all, just pure cleaned, bright copper. If solder is left over the traces that are under the solder mask, it will melt when board is reflowed or wave soldered as you said. That would not be a good thing. Solder mask should adhere to the copper well and not be affected by process temps much at all. Regards, Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, Michael Sent: Tuesday, May 08, 2007 10:21 AM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Wee: A fused Sn/Pb board is normally covered by soldermask. If not you could obviously have a real mess at wavesolder. The problem with a conventionally built fused Sn/Pb board i.e. circuitry is fused Sn/Pb, is that during reflow and/or wavesolder the Sn/Pb melts under the mask. This can cause adhesion failure of the soldermask to the Sn/Pb. It is especially true for larger features, ground planes, etc. If the board is then washed the condition can be aggravated by the chemistry and spray impingement resulting in additional loss mask or entrapment of wash residues. This was one of the drivers for going to a SMOBC style of construction, no melting metal under the mask. Regards Michael Barmuta Staff Engineer Fluke Corp. Everett WA 425-446-6076 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei Sent: Monday, May 07, 2007 5:37 PM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Thanks for the responds. From what I have gathered, fused SnPb can also have solder mask on them. My initial understanding or interpretation was that HASL finish is for SMOBC while fused SnPb finish is for board without solder mask. Regards, Wee Mei ________________________________ From: TechNet on behalf of Dehoyos, Ramon Sent: Mon 5/7/2007 10:15 PM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Wayne: Mostly copper with SnPb over it on some slivers. Pure copper from geometries such as traces and with SnPb such as pads. The slivers can be very small or very large. It depends on how it was removed. Large by hand and small by pumice spray. If they break off and wash away, no problem. If they partially break off and stay, they may shorten geometries. Other name for them is inclusions. Ramon >>>>> --------------- <<<<< The edges at the top will break off as slivers. | | | | | | | | ------- -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer Sent: Monday, May 07, 2007 9:53 AM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Ramon- But it was the SnPb which had slivers, and if that is chemically etched away, then what are the slivers made from? Wayne >>> [log in to unmask] 5/7/2007 9:16 am >>> Wayne: That is affirmative. SnPb is removed from everywhere except the pads, lands and anything else that needs solder over the top of copper. At this time bare copper is oxidized and needs to be cleaned by hand or spray so that SMOBC can adhere to it and slivers brake off. Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer Sent: Monday, May 07, 2007 8:56 AM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Ramon- What is it that needs mechanical removal? The oxidation of the copper traces due to selective SnPb removal? Wayne >>> [log in to unmask] 5/7/2007 8:46 am >>> Fused solder is more expensive and it takes about 5 more steps. When the SnPb is used as etch resist, as Wayne mentions, to pattern the outer layers and plate the pads and lands, the etching is not vertical so there is some underetching. slivers are formed at the top edge of the geometries. Later the traces have the SnPb taken off. So prior to having the solder mask applied, the copper traces are dull due to oxidation from etching the SnPb off which needs to be mechanically removed, leaving possible inclusions partially broken off. It can be a messy situation. Pads and lands are left with the solder over them which is later on fused by reflow oven. Thus the name fused solder. Most companies use HASL very few use Fused solder. Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer Sent: Monday, May 07, 2007 8:14 AM To: [log in to unmask] Subject: Re: [TN] What is the difference between Fused SnPb and HASL? Werner is quite correct but only mentioned the metallurgy, not the ramifications for processing. HASL is a quite obnoxious process in terms of board stress during application, but most non-aggressive board constructs can handle it: The panel is plunged into a vat of molten solder and then withdrawn while being blown off with very hot air. The deposits are lumpy, and start giving problems for smaller parts. Fused SnPb is just convection heated to slightly above the melting point--no thermal shock. Also the deposits are extremely even, so very fine pitch work is no problem. However, the normal way of achieving Fused SnPb is to use the plated SnPb for the final etch resist. This means that if you have a board with a solder mask, then the SnPb will be under the mask, which will greatly reduce its effectiveness. Wayne Thayer >>> [log in to unmask] 5/6/2007 9:39 pm >>> Hello, I come across QML vendors that state their finish system : HASL, Fused Solder, while some only states : HASL. I know that HASL stands for "Hot Air Solder Leveling", what then is fused solder? There must be some difference between them - what are they? Thanks and regards, Wee Mei --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the 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