Hot answers tagged

25

Sounds like a classic cold solder joint. This happens when the solder and pad are insufficiently heated (time or temp), or the surface is not clean, and the wetting action does not occur properly. If you use a meter to measure from one point to another on the solder itself, it should conduct, but between the solder and pad, there is not actually a good ...


24

Commercially there are two main soldering methods - reflow and wave. "Manual" soldering may still be used to add selected mechanically complex or large parts but this would be rare. "Manual" soldering could include the use of "robots" for the excessively keen. Wave soldering involves literally passing a wave of molten solder along a carefully preheated ...


20

There is no generic answer, it all depends on the components involved, let me add a few things to watch out for, and collect for the convenience a few more from the comments. First of all, read the datasheets of all involved components, what they say about reflow in general and a second reflow possibly. A lot of things will not be specified in the ...


19

My guess would be that the copper board is not being given enough time to heat up. Due to its thermal mass the copper heats up much more slowly than the solder, and the solder melts before the board reaches the correct temperature. If you choose a smaller piece of copper, or an etched PCB with less copper on it, or leave the copper board in the reflow oven ...


19

Lots of people use toaster ovens and electric fry pans for reflow. It can get a little touch and go with lead-free solder, and I recommend leaded solder. Large kitchen ovens likely don't have the oomph to bring things to temp fast enough, and your IC's may not tolerate the slow temperature profile. I think whatever appliance you use, you should dedicate ...


16

Because the method you describe, and it's advantage, is really a disadvantage. Not only is it harder to place smd parts on unevenly tinned pads, it prevents the main advantages of solder paste. The first is that solder paste holds a piece in place, ever so slightly, before being reflowed. It is a paste of tiny solder beads and flux. The smd parts are ...


16

Can you? Yes. Will it work every time... Maybe not! There are two reasons for this. Temperature profile and timing. Reflow is done using two temperatures, a pre-soak temperature and a reflow temperature as shown below. As such, you REALLY need to use two ovens to do this right, quickly switching it from one to the other after the pre-soak time. ...


14

42/58 Tin / Bismuth is not unknown as a low temperature solder but has issues. While widely used for some very serious applications (see below) it is not a mainstream industry contender for general use. It is not obvious why not given its substantial use by eg IBM. Identical to the Bi58Sn42 solder you cite is: Indalloy 281, Indalloy 138, Cerrothru. ...


14

Doing some research indicates some effects which might happen: Crystal oscillators show a decaying frequency deviation after reflow soldering. This might not be relevant for your board and doing two reflows shortly after the other shouldn't make much difference. The effect takes several days to decay. Which is interesting if you think about calibrating the ...


13

Reflow soldering techniques are used for surface-mount parts. Whilst most surface-mount boards can be assembled manually using a soldering iron and solder wire, the process is slow and the resultant boards can be unreliable. Modern PCB assembly facilities use reflow soldering exclusively for large-scale production, with pick and place machines putting the ...


12

Have you ever done any hand-pick-n-place work? You push the component into the solder paste, and it is this paste that holds the components in place when you sneeze over it or otherwise are handling the populated (but as yet not reflowed) PCB. With the solder already melted you don't only miss the 'gluing'. The flowed solder will have made small 'hills' on ...


11

What I do for prototype boards that I'm soldering by hand is to put a large hole in the pad and feed solder into it with the soldering iron. 2 mm works well. Solder the other pins first, so that the chip is fixed in position. The flux in the solder will be sufficient. Number of holes depends on the size of the pad. One is usually sufficient. You need a ...


11

It's amazing how easily solder (or other metals) can look clean but due to a thin layer of contaminant or oxidisation when you probe them you don't get an easy contact (you have to wiggle and press harder). This is why sharp probe tips are so important. Flux cleaner/Ethanol/Cotton buds are good to have handy also.


11

Both approaches are valid. Hand assembly would require that the paste mask for the SMT devices prevents putting any paste on the thru-hole pads at all. Then you use wire solder as usual during the hand assembly phase. Thru-hole devices can be soldered in the reflow oven; this requires a technique called "paste-in-hole" — but it doesn't work with all ...


10

I've heard bad things about desktop ovens like this. They don't necessarily have the oomph to get the job done correctly. Saying "I turned knob X to temperature Y and waited Z minutes" does not mean that you have any idea what's happening to your board. The only reliable way of knowing would be to measure, maybe with a thermocouple in contact with the ...


10

There are several reasons to put the alumina (white) side down. For small production/hobby runs it may not matter. You can tell if the resistor has been overloaded for whatever reason as the passivation/element color will generally change under high continuous heat. Depending on the technology, the contact dimensions may not be the same on the top as on the ...


9

First, for these small apertures, a 3-mil stencil thickness would work better than the 5-mil. OSH Stencils offers both. The extra thickness adheres more to the solder, lifting it from the PCB. Also, even when it works, the thicker stencil can leave too much paste on the pads. Other than that, I recommend a few things: Surround your pcb with other material ...


8

What you're most likely experiencing is the flux or similar chemicals which are preventing you from properly touching the conducting solder. Using alcohol will help you remove them. The solder itself conducts (unless it doesn't make proper contact), it's just that your instrument isn't connecting to it directly as it should.


8

This depends entirely on the board fab and the assembler. 0.5mm pitch components are common (MSOP-10 et al). Depending on the manufacturer they may recommend as big as 0.4mm pads, meaning you have only 0.1mm gap between the pads! I would personally ignore such advice as 100µm enters the realm of "special" board fabbing technologies. If you make the pads 0.3 ...


8

0805 resistors are fine without adhesive, in my experience. That's with 63/37 solder paste. This site contains the following claim: Most surface mount components will be held in place by the surface tension of the liquid solder alone when run through the re-flow oven inverted. The weight limit of the parts that can be processed on the underside during ...


8

You are worrying needlessly. SMT reflow followed by hand (or wave) solder for the through-hole components is the normal way of doing things. (Speaking as someone who used to run an in-house PCB build shop) If you have SMT pads very close to PTH holes on the same track / plane, there should be a solder-resist barrier to stop the solder flowing down the holes....


7

I don't know what the minimum is, but I recently worked on a design with 0.4mm pitch pads. The pads were 0.23mm. So the pad edge to pad edge dimension is only 0.17mm, which is around 6 or 7 mils. You might be confused in your terminology. In a solder-mask-defined pad, the copper pad is larger than the opening in the solder mask. So the solder mask defines ...


6

While going green is a laudable goal, the real reason most firms go led free is because of legal requirements in places like Europe or California (USA). If reliability is more important than green then why not stick with leaded solder, assuming of course that you are not requires by your customers to provide lead free or ROHS compliant product. With lead ...


6

To get the most dissipation from the pad it needs to be connected to a decent amount of copper. This is usually the ground plane, so place vias (no thermal reliefs) from the pad (or surrounding area - see document linked to below) to the plane. As Leon mentions, putting one large hole in the center of the pad can make it possible to solder it by hand ...


6

In general, reflow soldering would work w/o solder resist. You might get a higher incidence of solder bridges without solder resist (solder mask) than with it. Among other things, the incidence of solder bridges depends on the pitch (spacing) between the pins of the ICs you’re using. Fine pitch pins are easier to bridge. For example, you’d get more ...


6

Heatgun with aluminum foil warped around the rest of the board loosely, to act as a heat shield. You only want to heat the bad chip. No need to reflow everything else. If there is anything on the other side of the board, that might be an issue. This is just based on what I've read, no personal experience on this. The reason that the chips don't die when ...


6

It's perfectly possible to reflow your motherboard, but you have to do it really carefully to avoid destroying it. Several things can go wrong during soldering: thermal stress caused by different parts of the board being at different temperatures, and chips getting too hot. The reflow soldering process is designed to avoid these problems. This is the ...


6

Reflow for many packages just works better when the IC's can sit flatter on the board, and in paste. Try teetering a 100 pin package on the nicely rounded-over edges of hard solder, and see what happens. Your parts will just skid right off the pads before the solder melts. Less precision than you think is required for positioning IC's, as the surface ...


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