Nichi's from Mouser

[Neo2_000]

Just got my bag of Nichi's from the Mouser in the US.

Some of em are a bit taller than expected - especially the 470x25v ones but overall I'm pretty happy.

Been beat up a bit lately - a couple of losses after frying a single joint on two occassions, so it was good to have a few wins - a Pentium 4 AOpen MX46L among others.

The failures again have been caused after attempting to clean the holes of solder and my unregulated Scope Iron does nothing to help. You might have no troubles with clearing 20 caps but it only takes one bad joint to get you.

After checking out some posts here, I think I will avoid forcing stubborn joints in future - as one member said, so long as you can clean one hole you can still comfortably coax the new cap through the stubborn joint.

Certainly a better outcome than killing the board.

I have improved my dental pick - it was too long and thin, so I shortened it some so it is now a closer match to the lead diameter. Now any penetration creates a hole of sufficient diameter for the lead.

Gonna get some better glasses and a good iron. Hopefully all this will prevent any further disasters.

Whats the deal with the hot air tools on some of the desoldering stations I have been looking at? What is this used for?

[willawake]

yes i appear to have also nuked my first board due to either overheating two pads and/or forcing caps in these two places.

so long as you can clean one hole you can still comfortably coax the new cap through the stubborn joint.

this is indeed correct and i think also in my case tiredness was a factor. I need to keep this in mind and as you indicate to think about each cap in turn and employ different techniques depending on the difficulty encountered in clearing the holes.

regarding hot air pencils, i have no experience but as i have understood it is possible to remove and install smd components which are attached by two solder pads using a normal iron, if you do not have access to a hot air pencil. But when you are dealing with chips with many pins you really need a hot air pencil to remove/install them cos you can heat up many solder pads at one time. Also some smd components dont like the heat of an iron and also solder paste which is used with hot air pencils makes nicer joints.

might even be good for caps as well.....but the cost of a full soldering/desoldering/hot air rework station is a hell of a lot.

KC8 noted a while back that he heats up boards before working with them using a hot air gun. This is interesting and if we could find a suitable paint stripper gun or something which could be obtained at low cost but safe to use on boards, it may assist with working on boards that have difficult solder on them.

i was also looking at airbaths at one point and seeing if they would be something within the budget.

http://www.zeph.com/airbathseries.htm

this article is interesting because it talks about the importance of pre-heating boards before reworking them. of course it on the site of the same bloody company as sells the airbaths but makes sense.
http://www.zeph.com/paradigm.html

otherwise we have the diy hot air pencil from desoldering iron and aquarium air pump.....lol....

http://www.usbmicro.com/odn/documents/46.html

[Neo2_000]

Thanks once again willawake. You certainly are a wealth of information.

While I did not want to admit it, tiredness was definitely a factor in frying my two failures as well. It was well after midnight and I should have been in bed long ago.

Pays dividends to approach the task while you are fresh as you say.

I have a hair dryer which I bought at a garage sale for $5. I use it to wrap heat shrink. Wonder how this would affect the process?

[willawake]

I have a hair dryer which I bought at a garage sale for $5. I use it to wrap heat shrink. Wonder how this would affect the process?

it is indicated that burns would occur to someones head at 60 degrees Centigrade so it is doubtful whether a hair dryer would have enough temperature to be of use.

The following document regarding ceramic chip capacitors is quite interesting and indicates that preheating of circuit and capacitors to 150°C is recommended. It emphasises that proper preheating is essential to prevent thermal shock cracking of the capacitor.

The circuit assembly should be preheated as shown in the recommended profiles at a rate of 1.0 to 2.0°C per second to within 65 to 100°C of the maximum soldering temperature. Solders typically utilized in SMT have melting points between 179°C and 188°C. Activation of rosin fluxes occurs at about 200°C. Based on these facts a minimum peak reflow temperature of 205°C to 210°C should be established. A maximum peak reflow temperature of 225°C should be adequate in most circumstances. Many reflow process profiles have peaks ranging from 240°C to 260°C and while ceramic capacitors can withstand soldering temperatures in this range for short durations they should be minimized or avoided whenever possible.

http://www.johansontechnology.com/technicalnotes/srq/

the thing is if we are considering heating large areas of the boards using a heat gun then the thermal precautions for nearby components will have to be considered also.