Addressing Solder Bridge Formation Beneath SMD Components During DIY Reflow

[Shubham]

When reflowing PCBs in a DIY reflow oven, I'm encountering issues where solder bridges are forming beneath SMD components, making it difficult to identify the faulty location. What could be causing this problem, and what steps can I take to prevent or address it effectively?

[48X24X48X]

How does your paste application on the pads looks like?

[MR]

This looks like there's a carrier where the solder attached, maybe some small piece of wire on it?
The bridge looks too straight, according to my experience this is impossible to happen with standard quality solder paste without a carrier.

Clean the PCB and ensure that the components are OK before pick and placing them. And check if there's dirt/small "hair" like threads in the paste

[Kean]

Those look like 0805 parts, so this is quite unexpected.  The thin straight bridge is very unusual.
Solder paste application doesn't look excessive, but hard to tell without better photos.  Parts at the left of the photo look hand soldered or reworked.

I would guess that this is due to poor quality, expired, or contaminated solder paste.

What paste are you using and what reflow profile?  Have you confirmed the reflow temperatures on your DIY oven?

[Matt-Brown]

looking at the capacitors and  the sot223 it looks to me like the reflow profile is not correct. probably heating too fast, and also too short a time. the flux is boiling and spitting causing bridging need a slower ramp time

[jmelson]

Poke at that bridge with a soldering iron.  Does it melt right away?  I am guessing not - it is a metallic hair either on the blank PCB or on one of the components.  Is this the only one of these bridges, or are there more of them?  Look carefully for metallic contamination when the boards have paste applied or when they are are stuffed.  I use GC10 paste and it is remarkable in eliminating bridging.
Jon

[MarkT]

Seems a bit heavy with the paste - are you using a stencil?

[Doctorandus_P]

If this bridge persists even after de-soldering, it looks more like an etching fault on the PCB itself. I once had a fault because of a hair on a matrix PCB (during lighting / development of the etch resist) and this shorted about 6 or 7 pads.

Another factor not mentioned earlier is the close proximity of the pads. usually there is more space between the pads under the resistors.

Wrong heating profile is also a good point. Maybe try another brand of solder / flux too...