The FLIR TAU / Tau 2 …. How a $2 obsolete component could ruin your day ! - Page 1
Forum section: electronics / general

author: Fraser
author_rank: Super Contributor
timestamp: April 04, 2025, 12:50:01 pm
content: I am currently in the process of repairing a FLIR TAU 2 640 and thought I would share my experience here.The TAU 2 640 core has come to me for repair with the stated fault being “FFC flag operating, but no thermal image present” I agreed to take on the job but warned that there was no guarantee that I could repair the core as some parts are unobtainable. When I said that, I was thinking about large specialist IC’s and not what I am now having trouble sourcing …. A humble connector.I inspected the core for evidence of damage and found none. With these cores used on drones, it is good to check for exterior signs of impact as that can assist in the diagnostic process. It was then time to open the core by removing its rear cover and accessing the rear (processor and power supplies) PCBA. It was at this point that a fault became evident. As I gently tilted the PCBA away from the cores chassis, I could see the FPC pulling the associated ZIF connector partially off of the Processor PCBAThis was not good to see but might actually be the fault that I was hunting. This core had previously been opened by the owner so I cannot be certain that this is the original fault. The Microbolometer FPC is very stiff and great care is needed when removing the processor PCBA from the core chassis to avoid stressing the ZIF connector to which the Microbolometer FPC connects.The next step was to try to release the locking clamp on the ZIF connector to release the FPC and separate the processor PCBA from the core. Well that did not go so well as the act of lifting the locking clamp was enough to cause the ZIF connector to completely detach from the PCBA. All was not lost though as none of the processor PCBA pads were damaged and even the ZIF connector appeared undamaged but little did I know this repair was going to turn really ugly. Many techs, including myself, would think that a detached ZIF connector is no great drama provided the PCBA pads remain undamaged. Well that would be true in most cases but read on to discover the challenge that I face.ZIF connector location : the 28 pin ZIF connector is mounted to the processor PCBA adjacent to the processor IC. It is mounted so close to the processor that a soldering iron does not fit into the available gapNo problem you think, “use hot air”…. well that was my thought as well. The risk of using hot air is that it will get everything in the area around the ZIF connector very hot and the PCBA has a solid copper pour around the area for thermal transfer reasons. The ZIF connector is designed to withstand 250 Celsius for 10 seconds and its pin connections to the PCB would be hard to access with hot air due to the narrow gap available. That area of the PCB was going to require preheating and quick work with the hot air pencil. Not an impossible task, but a challenge all the same. I decided to use Loctite Multicore LMP Lead/Tin/Silver solder with a melting temperature of around 180 Celsius. This was confirmed by test using the hot air pencil on a sample of the solder. The PCBA pads were easily stripped of their awful lead free solder and re-tinned with LMP solder in preparation for the ZIF socket reflow task….. but there was a problem. Upon close inspection of the ZIF connector I could see that it’s rear contacts did not sit flat on a surface. The connector was not bent, it was warped at one end, creating a hump ! There is no way that this occurred when the connector came away from the PCB so I suspect it was a faulty connector from new and likely was not properly soldered to the PCB as a result. A poor solder joint could cause the fault on the core. It is a new old stock core that failed after only 20 minutes of use.So what do you do when a tiny ZIF connector is warped ? You source a new one of courseWell yes, if it is still available….. and I discovered that the connector was EOL in 2022 with no alternative knownNo problem, there is bound to be old stock around and on eBay right ? Well nope, these connectors are rare indeed. No problem, I will just find a similar connector from another Manufacturer….. nope, nothing similar foundThis connector was a specialist product intended for use in confined spaces so it is very low profile and very short in breadth. All standard ZIF connectors are too large in breadth to allow fitting of the pretty inflexible FPC so whilst they could be used, the case on the TAU 2 640 could not be reassembled. The TAU 640 is a different PCBA layout to the TAU 320 so an alternative connector might be useable on the less crowded 320 type core.The ZIF connectorI needed to identify the ZIF connector model before I could search for a replacement. It was helpfully marked up as “HRS” and “28” so I was looking for a 28 contact low profile Hirose ZIF FPC connector. I determined that it was a 0.5mm contact pitch. I searched the current Hirose catalogue and found nothing useful. Further deep Google searches revealed the connector to be an obsolete model FH19SC series 28 pin connector designed for specialist applications where small size was important. The whole FH19S and SC series was declared “End of Life” in 2022. Hirose stated that it was manufactured on old equipment and was in low demand, so deleted from their production. They stated that no Hirose alternative existsAs a “low demand” specialist connector, I knew it might be hard to find as NOS, and I was correct. Only Chinese sellers had stock and they would take time to deliver to the UK and were relatively expensive. (More on that later)I revisited the original ZIF connector and looked at repairing it. I used some heat and appropriate pressure to try to flatten the “hump” but it was only a partial success. I then attempted to refit the ZIF connector with a professional hot air pencil and all appeared to go well. That was until I inspected the solder joints under a microscope. The contacts in the area of the hump did not look properly soldered and the whole darned connector had moved sideways slightly on the PCBA padsI decided further rework was needed. I could not get a soldering iron onto the poorly soldered contacts and the connector misalignment concerned me. I tried another hot air rework run on the connector whilst pressing down on the area of the hump. Disaster struck… the connector both cracked and melted !It was “game over” for the connectorWhen stuff like this happens, you question why you took on the Job in the first place. I was not a happy bunny as I knew I had no backup plan for this eventuality. Communications with the owner of the core had been ongoing throughout the rework process and he was aware of the risks. He is what I class as a “good” client as he was grateful for my efforts with no issues regarding the failed rework attempt. He has two damaged ZIF connectors that he is sending to me in case I can repair them for use on his core. The locking clamp has come off of them so they are a bit of an unknown quantity at the moment, due to the clever connector design that retains the locking clamp. I also “bit the bullet” and ordered a new FH19SC 28 pin ZIF connector from China. It will arrive towards the end of April. If the donor connectors cannot be repaired I shall re-attempt repair of the TAU 2 core once the Ex China connector arrives.So be warned, if you damage the HRS FH19SC 28 pin connector to the microbolometer board in your TAU, you are in for a painful experience when trying to repair it.I will upload some pictures of the PCBA and ZIF connector later.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 04, 2025, 02:16:30 pm
content: Pictures of the TAU 2 640 core and connector damage.

author: Fraser
author_rank: Super Contributor
timestamp: April 04, 2025, 02:17:16 pm
content: ZIF connector detailsThe connector used in the TAU cores is theHirose FH19SC-28S-0.5SHThe TAU1/2 320 and 640 both use the same connector.

author: Fraser
author_rank: Super Contributor
timestamp: April 04, 2025, 02:24:11 pm
content: The damaged connector placed above one mounted on the processor PCB of a TAU 320 core. There is no issue with access to the ZIF connector pins on a TAU 320 PCBA for hand soldering. The situation is very different on the TAU 2 640.Fraser

author: MrSheep
author_rank: Frequent Contributor
timestamp: April 04, 2025, 06:44:42 pm
content: Wow what a headache. Usually when I run into these issues, I order spares just in case I ruin it on the first try. I wonder if u can solder the pins using a microscope and bent conical tip. U will get bridging but if the iron can reach down there, flux and quality solder wick should do the trick. Reminds me of soldering broken micro usb connectors.

author: gamerpaddy
author_rank: Regular Contributor
timestamp: April 05, 2025, 06:46:32 pm
content: i would try replacing the solder on those pads with low melt / leaded and put the whole pcb on a hotplate, not even hot air.you gonna melt that connector in no time when trying to use a iron

author: defplayr
author_rank: Contributor
timestamp: April 05, 2025, 11:15:25 pm
content: I would be tempted to 'jump connect' to a compatible ZIF connector and epoxy that connector to the board, in a suitable place for the ribbon to connect without strain.i.e. jumper wire from each pad to the relevant solder pin on the ZIF, epoxy those wires to the board, then epoxy the ZIF in the correct orientation. Thicker wire for current, and thin for signals. Practically speaking it would be easier to solder to the ZIF first, trim the wires, and then offer up to the board.

author: Fraser
author_rank: Super Contributor
timestamp: April 06, 2025, 12:37:38 pm
content: I considered moving the ZIF connector as suggested, but there is no room for that to work in the TAU 2 640 and the Microbolometer FPC cable is anything but flexible !This is why I have had to come up with a plan to fit the connector with a hot air pencil. I am using LMP so,dear that melts at 180 Celsius and the connector can withstand 250 Celsius. I have to preheat the PCB to speed up the soldering process and managed to do this before with the faulty ZIF connector. It was the hump in that connector that defeated me. I used 300 Celsius to remove the faulty connector as quickly as possible and it melted so I have to be careful. It is possible however. I am fortunate to own a JBC hot air rework station that has very accurate temperature control so when it says 250 Celsius at the output air stream, it really is close to 250 Celsius. I even considered solder with a lower melting temperature of 150 Celsius and I may well look into that and it’s properties whilst I await the arrival of the new ZIF connector from China.The client is commercial so I cannot get too adventurous with solutions as I do not know where this “New old stock” camera will be used. Keeping it “factory” is the safest option.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 06, 2025, 01:23:59 pm
content: I have been browsing the various low melting point solders and considering trying something with a lower melting point than my Leaded LMP 180 Celsius usual choice. I see that there is solder paste that melts at 158 Celsius and another that claims 138 Celsius. These are lead free Tin Bismuth alloys and I normally only use Bismuth for removing delicate ICS by alloying it to the unleaded solder to ease removal. Does anyone have any experience or comments on using 138 Celsius or 158 Celsius Tin Bismuth solder alloys please ? I should state this this is proper solder fir electronics and not “ChipQuick” which is what I use to remove some IC’s.The 158 Celsius solder appeals to me but I truly dislike unleaded solder unless I have no other choice. This could be such a case with the thermally delicate ZIF connector. 138 Celsius is getting close to ChipQuick and I am not so sure about using that to solder a connector to a PCB.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 06, 2025, 05:51:42 pm
content: I have ordered some Best branded low melting point solder paste to have a play with. If it performs well in tests on scrap laptop PCB’s I will consider using it on the TAU 2 core. It is a Tin (48%)/Bismuth (52%) alloy with a stated melting point of 138 Celsius. This is new territory for me as I tend to be a traditionalist and use Tin/Lead or Tin/Lead/Silver alloy but I see that work on some modern mobile phones needs these low melting point solders. The situation with the TAU core is not that dissimilar.If nothing else I will learn more about these Tin/Bismuth allow low temperature solders and how they behave in use. I would like to play with some Indium alloy solder as well but that stuff is expensive.Fraser

author: EE-digger
author_rank: Frequent Contributor
timestamp: April 09, 2025, 05:01:12 pm
content: Been through 50 years of solders, fluxes and contamination. Now I can solder with whatever the hell I pleaseI recall a lead free that impressed me with bright joints, good wetting. It seems to me it had a "splosh" of Germanium in it. Google immediately returns AIM SN100C and that number rings a bell. Shiny joints like the best leaded ones.Personally, I wouldn't bring unleaded within a country mile of a repair. It's the source of every ruined, hi density connector I've seen in the last 20 years.Is there any chance of "de-warping" your connector with carefully applied hot air?Whatever you do, when you have good mechanical integrity, I'd lock the whole thing down to the PCB. Have used UV cured acrylic for this and my favorite is to place small shreds of hot glue over the components and blast it with a hot air gun (not soldering temp).The hot glue runs like water, grips the PCB like nails and holds everything down. If nothing else, it kills any shock or vibration related failures. It has an unbelievable grip that hot glue from a gun never achieves.

author: Fraser
author_rank: Super Contributor
timestamp: April 09, 2025, 06:26:23 pm
content: Thanks EE-Digger.I am suitably cautious about using the unleaded Tin/Bismuth solder but thought it worth taking a look at in case it is worth using. It arrived today so I will have a play with it out of interest in its properties. I still like good old fashioned Multicore (now Loctite) LMP Tin/Lead/Silver solder that is very predictable and melts at 183 Celsius. I have never had problems with that solder and achieve beautiful shiny jointsSadly the original warped connector was destroyed after I refitted it, had connection issues and I had to remove it from the PCB. I had tried flattening it prior to refitting it but it is a fragile material and all the reworking eventually melted it. A replacement, brand new, connector is currently on its way to me from China and I shall be very careful to keep the hot air temperature below the connectors maximum temperature tolerance of 250 Celsius whilst fitting it. The PCB will be preheated and quality gel flux will be used.You are absolutely right about needing to lock the connector down to the PCB. One of the connectors front solder pads was torn off in the original failure and I will need to secure the new connector very well indeed. Thank you for the suggestion of hot melt glue. I will roughen the PCB surface either side of the connector to provide a good adhesive key.Fraser

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: April 09, 2025, 08:04:36 pm
content: Quote from: Fraser on April 06, 2025, 05:51:42 pmBE ADVISED; BISMUTH IS A METALLURGICAL NIGHTMARE.It will "poison" the metallurgy of any other solder you use the tools on, causing weird crystallization and behavior.USE DEDICATED IRON AND TOOLS, DO NOT MIX WITH LEAD OR LEAD FREE.Also most standard fluxes don't work super nicely to improve wetting, not sure why.I have hard banned bismuth solders from my lab and had to throw some away at work that snuck in.

author: Fraser
author_rank: Super Contributor
timestamp: April 09, 2025, 08:13:55 pm
content: ArsenioDev,Many thanks for this warning. I was going to use a cheap Chinese soldering iron and tips for testing the Tin/Bismuth solder and hot air was going to be used on the PCB connector so no iron would be involved.I like to understand what options exist for “difficult cases” and the Tin/Bizmuth is just another tool to have in the back pocket for those really difficult scenarios where nothing else will work. It is a bit like conductive glues….I would not use them except where there is no other option and even then would use them under protestYour comment regarding the poor performance of the flux is very interesting.I had previously thought that Tin/Bismuth and “ChipQuick” could be cleaned from a soldering iron tip with standard “Tip cleaner” paste and plenty of wiping on a brass scourer. Is this not the case ? I shall have to do some research on Bizmuth.Be assured, I am currently intending to solder the connector using good old fashioned Multicore LMP Tin/Lead/Silver solder.Thanks again for this very useful warning.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 09, 2025, 08:45:07 pm
content: An interesting read…..https://www.indium.com/blog/has-the-time-come-for-tin-bismuth-solders.phpSo the presence of lead when soldering with Tin/Bismuth solder has a very negative effect on the solder joint and can lead to a eutectic phase point of only 96 Celsius and poor thermal cycling performance. Interesting stuff

author: Fraser
author_rank: Super Contributor
timestamp: April 09, 2025, 08:51:37 pm
content: More interesting reading….https://www.brazing.com/products/Soldering/TinBismuthSoldering.aspxThe Reflow instructions are interesting…….ReflowHeating Stage: Linear ramp rate of 0.5° - 1°C/second allows gradual evaporation of volatile flux constituents and prevents defects such as solder balling/beading and bridging as a result of hot slump. This also prevents unnecessary depletion of fluxing capacity when using higher temperature alloys.Liquidus Stage: Peak temperature of 25° - 45°C above the melting point of the solder alloy is needed to form a quality solder joint and achieve acceptable wetting due to the formation of an intermetallic layer.Cooling Stage: Rapid cool-down is desired to form a fine grain structure. Slow cooling will form a large grain structure, which typically exhibits poor fatigue resistance. The acceptable cooling range is 0.5° - 6.0°C/second (2° - 6°C/second is ideal).