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Electronic devices have been designed with a board known as PCBA which holds all the electronic components together to complete the conductivity circuit. Manufacturing the circuit board primarily is made up of an etching process where a copper sheet is plated into a non-conductive substrate material and holes drilled onto the end product board. The purpose of the drilled hole is to ensure conduction between the board’s copper layers and the components that are fixed in the board. Remember that there exist different types of circuit boards with different layers, but the simplest form of the board that utilizes the through hole assembly technology only has a top and a bottom layer. The drilled holes will never be conducive until an advanced process known as electroplating that triggers the conductivity is utilized. This advanced process involves the application of a thin copper layer on the walls of the drilled holes. The electroplating of the drilled holes is what leads us to what we refer to as plated through holes (PTH). This article will focus on the PTH PCBA and how we can compare it to the NPTH PCBA. Let us get started!

The difference between PTH and NPTH

In PCBA, the definitions of the two are different, PTH stands for plated through hole while NPTH stands for non-plated through hole.

PTH is where the drilled hole has a solder stop mask and copper pad designed to be larger than the diameter of the hole which is about 6 mil than the designed minimum width.

For an NPTH, the plated copper pads appear tinier than the drilled hole and in other cases, the copper is absent while its copper overlay on the pads exceeds the drilled hole size with a buffer zone of size 6 mil separating the slot and copper

NPTH & PTH PCB Drilling Rules

The existence of holes is to ensure the smooth progress of PCB assembly projects. For this reason, we need to consider the design and manufacturing rules of PTH and NPTH, which will directly affect the assembly quality. The following are the drilling rules of the two listed by FS Technology:

Non-Plated Through Hole Drilling Rules:

Minimum complete size of the hole should be 6 mil;
The minimum hole edge-to-edge clearance should be 5 mils from the total placed surface elements.

Plated Through Hole Drilling Rules:

The minimum size of the annular ring should be 4 mil
The minimum size of the complete hole should be 6 mil
The minimum hole edge-to-edge clearance should be 9 mils from the total placed surface elements.

In general, you should consider the size of the drilled hole, the type of vias, the spacing, and the aspect ratio during the process of drill hole DFM regulations and guideline development. For example, if your intention to set the DFM rules is to save space, then you will have to make use of the via-in-pads.

The difference between PHT and NPHT in the manufacturing process

Apart from the difference noted in the definition of the two, we can differentiate the two through-hole processes based on the PCB-Herstellungsprozess. The PTH hole drilling occurs before the process of electroless copper while for the NPTH, the hole drilling process occurs after the board has undergone the process.

Defining the two is a very straightforward process, but implementing them in a PCB Montageprozess is what proves to be a bit difficult. For example, if a PCBA manufacturer receives a file that has a copper overlay pad wider than the drilled hole but with the absence of the solder stop, the mask appears confusing. The manufacturer is tied between plating or not plating it. Therefore, it is a requirement that every PCB designer pays adequate attention to designed Gerber files before submitting them to the fabrication house.

From the feedback from most PCBA-Hersteller, if all the drilled holes have solder-stop masks overlay and are larger than the drilled hole then:

Those that are connected to the copper traces and have broader copper pads than the drilled holes qualify to be labeled as plated through hole;
Those without copper are labeled as Non-plated through hole.

PTH/ NPTH Typical Applications

These two through-hole technologies are widely used in PCB assembly. PTH metal holes have two uses depending on their size. The larger aperture is used to solder DIP components, and the smaller aperture is called “via hole”, which is used to connect copper foil lines between PCB layers. The NPTH PCB may be used as a screw hole because there is no copper in the hole. The following are typical applications of PTH/NPTH:

Voltage Isolation Air gaps for milling slots; This is because they can be easily replaced when electrical arcs that burn out components occur.
Rectangular components connection; such components include DC jacks which require a reliable connection joint.

Plated Through Hole Assembly Process

FS Technology inserts the leads of DIP components into the corresponding PCB plated through holes through automated equipment:

Diodes & Resistors Axial Insertion Process
Electrolytic Capacitors radial insertion process
Odd form insertion process for connectors, transformers, etc.
Manual Process used for many other electronic components

After completing the insertion of components process, the soldering of the placed through-hole components is done by use of the following soldering processes and techniques:

Manual Soldering;
Intrusive Reflow-Löten oder Wellenlöten;
Selective Soldering.

Although SMT assembly is more in line with the needs of miniaturized electronic devices, THT assembly soldering can provide the advantage of stronger joints. This is simply because the leads of the electronic components are placed through the PCB.

Plated Through Hole PCB Assembly Failure

Through PCBA Fehleranalyse, we know that assembly is a complex and subtle process, and any mistakes in this process will lead to assembly failure. The following are the failures that may be encountered during the PHT assembly process of the PCBA factory:

Rissbildung im Fass
Mängel bei der Zusammenschaltung
Belastung durch thermische Auslenkung
Risse in der Folie

Aus der obigen Liste geht hervor, dass das größte Fehlerproblem, das bei durchkontaktierten Baugruppen auftritt, die Verbindungsfehler (ICD) sind. Diese entstehen durch mechanische Spannungen, die aus dem Unterschied zwischen dem Wärmeausdehnungskoeffizienten und dem System des PTH resultieren. Die Glasverstärkung des Fertigungssystems begrenzt die Materialausdehnung entlang der normalen X- und Y-Achse, so dass sich das Material entlang der verbleibenden uneingeschränkten Z-Achse schneller ausdehnen kann. Die Ausdehnungsbewegung führt zu adhäsiven Spannungen zwischen den Verbindungen und dem plattierten Kupfer, die zu einer Trennung führen können. Diese Spannung führt auch zu anderen Problemen, die bei der PTH PCB-Baugruppe.

Um solche Fehler zu beheben oder zu vermeiden, müssen Sie zunächst die beste Verkupferungsprozesse und Praktiken, und zweitens müssen Sie versuchen, die unten aufgeführten Lösungen zu adaptieren:

Achten Sie darauf, dass die Dicke des stromlosen Kupfers auf den miteinander verbundenen Kupferschichten gleich groß ist.
Vergewissern Sie sich, dass Sie eine solide Ablagerung von Kupferstrukturkorn haben.
Bei der Wahl des Harzmaterials sollte die Fähigkeit des Materials berücksichtigt werden, thermischen Belastungen standzuhalten, ohne sein Gewicht zu verlieren.
Stellen Sie sicher, dass Sie den Test des hohen Aspektverhältnisses durchführen, indem Sie die hergestellten Leiterplatten während der Prototypenbestückung wiederholten Erschütterungen aussetzen, um den Temperaturbereich zu kennen, in dem das Versagen der Leiterplatte auftritt.

Vorteile der PTH-Produktion

Prototyping-Verfahren speziell für die Breadboards
Ideal für PCB-Bestückungsprojekte in kleinen Serien
Wird verwendet, wenn eine robuste oder stärkere Befestigung benötigt wird, z. B. für Transformatorenbefestigungen.
Robuste und starke mechanische Verbindungen im Vergleich zur SMT-Montage.
Einfaches Reparieren und Ersetzen defekter elektronischer Komponenten mit der Hand statt des Austauschs ganzer Schaltkreise.
Das Verfahren ist sehr nützlich, wenn es um die Verwendung von sperrigen Bauteilen in der Schaltung geht.

Zusammenfassen

Bei der Durchkontaktierung werden Löcher auf der Leiterplatte gebohrt und galvanisch beschichtet, bevor die Bauteile angeschlossen werden;
PTH PCB hat breitere Kupferpads, während NPTH keine Kupferpads hat;
Die DIP-Bauteile werden entweder im axialen, radialen oder manuellen Bestückungsverfahren auf der Platine platziert;
PTH- und NPHT-Bauteile werden entweder durch Handlöten, Wellenlöten oder Selektivlöten in die Platine gelötet;
Unplattierte Durchgangslöcher haben eine Mindestgröße von 6 mil, während der Abstand von Kante zu Kante 5 mil betragen sollte.
Das plattierte Durchgangsloch hat eine Ringgröße von 6 mils, einen Abstand von Kante zu Kante von 9 mils und eine minimale Gesamtlochgröße von 6 mils.
Ausfälle können während der PTH PCBA-Verfahren aufgrund von Trommelrissen, Verbindungsfehlern, thermischen Ausschlägen und Folienrissen.
PTH und NPTH eignen sich für Anwendungen, die robuste Verbindungen, Prototypen und kleine Produktionsserien erfordern.